Showing posts tagged Mozilla

Using Sphinx in a Monorepo

Sep 25th, 2022

Sphinx Documentation Voltus Mozilla

Just wanted to type up a couple of notes about working with Sphinx (the python documentation generator) inside a monorepo, an issue I’ve been struggling with (off and on) at Voltus since I started. I haven’t seen much written about this topic despite (I suspect) it being a reasonably frequent problem.

In general, there’s a lot to like about Sphinx: it’s great at handling deeply nested trees of detailed documentation with cross-references inside a version control system. It has local search that works pretty well and some themes (like readthedocs) scale pretty nicely to hundreds of documents. The directives and roles system is pretty flexible and covers most of the common things one might want to express in technical documentation. And if the built-in set of functionality isn’t enough, there’s a wealth of third party extension modules. My only major complaint is that it uses the somewhat obscure restructuredText file format by default, but you can get around that by using the excellent MyST extension.

Unfortunately, it has a pretty deeply baked in assumption that all documentation for your project lives inside a single subfolder. This is fine for a small repository representing a single python module, like this:


However, this doesn’t work for a large monorepo, where you would typically see something like:


In a monorepo, you usually want to include a module’s documentation inside its own directory. This allows you to use your code ownership constraints for documentation, among other things.

The naive solution would be to create a sphinx site for every single one of these submodules. This is what happened at Voltus and I don’t recommend it. For a large monorepo you’ll end up with dozens, maybe hundreds of documentation “sites”. Under this scenario, discoverability becomes a huge problem: no longer can you rely on tables of contents and the built-in search to discover content: you just have to “know” where things live. I’m more than nine months in here and I’m still discovering new documentation.

It would be much better if we could somehow collect documentation from other parts of the repository into a single site. Is this possible? tl;dr: Yes. There’s a few solutions, each with their pros and cons.

The obvious solution that doesn’t work

The most obvious solution here is to create a symbolic link inside your documentation directory, say the following:

<root>/docs/module-1/submodule-a -> <root>/module-1/submodule-a/docs

Unfortunately, this doesn’t work. ☹️ Sphinx doesn’t follow symbolic links.

Solution 1: Just copy the files in

The most obvious solution is to just copy the files from various parts of the monorepo into place, as part of the build system. Mozilla did this for Firefox, with the moztreedocs system.

The results look pretty good, but this is a bespoke solution. Aside from general ideas, there’s no way I’m going to be able to apply anything in moztreedocs to Voltus’s monorepo (which is based on a completely different build system). And being honest, I’m not sure if the 40+ hour (estimated) effort to reimplement it would be a good use of time compared to other things I could be doing.

Solution 2: Use the include directive with MyST

Later versions of MyST include support for directly importing a markdown file from another part of the repository.

This is a limited form of embedding: it won’t let you import an entire directory of markdown files. But if your submodules mostly just include content in the form of a (or similar), it might just be enough. Just create a directory for these files to live (say services) and slot them in:


```{include} ../../../module-1/submodule-a/

I’m currently in the process of implementing this solution inside Voltus. I have optimism that this will be a big (if incremental) step up over what we have right now. There are obviously limits, but you can cram a lot of useful information in a README. As a bonus, it’s a pretty nice marker for those spelunking through the source code (much more so than a forest of tiny documentation files).

Solution 3: Sphinx Collections

This one I just found about today: Sphinx Collections is a small python module that lets you automatically import entire directories of files into your sphinx tree, under a _collections module. You configure it in your top-level like this:

extensions = [

collections = {
    "submodule-a": {
        "driver": "symlink",
        "source": "/monorepo/module-1/submodule-a/docs",
        "target": "submodule-a"

After setting this up, submodule-a is now available under _collections and you can include it in your table of contents like this:


:caption: submodule-a



At this point, submodule-a’s documentation should be available under http://<my doc domain>/_collections/submodule-a/index.html

Pretty nifty. The main downside I’ve found so far is that this doesn’t play nicely with the Edit on GitHub links that the readthedocs theme automatically inserts (it thinks the files exist under _collections), but there’s probably a way to work around that.

I plan on investigating this approach further in the coming months.

90 days out and in

Apr 16th, 2022

Mozilla Voltus Recurse

The 90 day mark just passed at my new gig at Voltus, feels like a good time for a bit of self-reflection.

In general, I think it’s been a good change and that it was the right time to leave Mozilla. Since I left, a few people have asked me why I chose to do so: while the full answer is pretty complicated (these things are never simple!), I think it does ultimately come down to wanting to try something new after 10+ years. I’ve accumulated a fair amount of expertise in web development and data engineering and I wanted to see if I could apply them to a new area that I cared about— in this case, climate change and the energy transition.

Voltus is a much younger and different company than Mozilla was, and there’s no shortage of things to learn and do. Energy markets are a rather interesting technical domain to work in— a big intersection between politics, technology, and business. Lots of very old and very new things all at once. As a still-relatively young company, there is definitely more of a feeling that it’s possible to shape Voltus’s culture and practices, which has been interesting. There’s a bit of a balancing act between sharing what you’ve learned in previous roles while having the humility to recognize that there’s much you still don’t understand in a new workplace.

On the downside, I have to admit that I do miss being able to work in the open. Voltus is currently in the process of going public, which has made me extra shy about saying much of anything about what I’ve been working on in a public forum.

To some extent I’ve been scratching this itch by continuing to work on Irydium when I have the chance. I’ve done up a few new releases in the last couple of months, which I think have been fairly well received inside my very small community of people doing like-minded things. I’m planning on attending (at least part of) a pyodide sprint in early May, which I think should be a lot of fun as well as an opportunity to push browser-based data science forward.

I’ve also kept more of a connection with Mozilla than I thought I would have: some video meetings with former colleagues, answering questions on Element (, even some pull requests where I felt like I could make a quick contribution. I’m still using Firefox, which has actually given me more perspective on some problems that people at Mozilla might not experience (e.g. this screensharing bug which you’d only see if you’re using a WebRTC-based video conferencing solution like Google Meet).

That said, I’m not sure to what extent this will continue: even if the source code to Firefox and the tooling that supports it is technically “open source”, outsiders like myself really have very limited visibility into what Mozilla is doing these days. This makes it difficult to really connect with much of what’s going on or know how I might be able to contribute. While it might be theoretically possible to join Mozilla’s Slack (at least last I checked), that feels like a rabbit hole I’d prefer not to go down. While I’m still interested in supporting Mozilla’s mission, I really don’t want more than one workplace chat tool in my life: there’s a lot of content there that is no longer relevant to me as a non-employee and (being honest) I’d rather leave behind. There’s lots more I could say about this, but probably best to leave it there: I understand that there’s reasons why things are the way they are, even if they make me a little sad.

Leaving Mozilla

Dec 21st, 2021


I’ve decided to leave Mozilla as an employee: my last day will be December 31st, 2021.

It’s hard to overstate the impact Mozilla has had on my life. In particular, I’m grateful for all the interactions I’ve had with the community: the opportunity to build technology for the public good with people around the world was unique and I’m really going to miss it.

Looking back over the past 10 years, I’m feeling pretty good about the impact I had through building better developer and data tooling: mozregression, Perfherder, Iodide and the Glean Dictionary stand out as particular highlights. Thanks to everyone who worked on those things with me! I am because we are.

Last Lecture

It’s become traditional in Data @ Mozilla for the person leaving to give a last lecture on their way out. I decided to give a talk on a specific area of focus for me over the last couple of years: documentation.

I’m not sure how comprehensible it will be to people outside of my particular context at Mozilla, but it seemed fitting to post it publically regardless.

I’m more convinced than ever that documentation is one of the keys to empowering people to make better decisions with data (no matter what their job title). I hope my efforts here have been helpful.

Joining the Community

After having spent a good chunk of energy on making it possible for people outside the Mozilla Corporation to contribute to our projects, I’m looking forward to seeing what it’s like on the other side of the fence.

I’m not sure right now exactly how active I’ll be, but I plan on sticking around on Matrix and Bugzilla, at least a little bit. If there’s anything I can help you with, feel free to reach out!

Learning about Psychological Safety at the Recurse Center

Oct 19th, 2021

Mozilla Recurse

Last summer, I took a 6-week sabbatical from my job to attend a virtual “programmers retreat” at the Recurse Center. I thought I’d write up some notes on the experience, with a particular lens towards what makes an environment suited towards learning, innovation, and personal growth.

Some context: I’m currently working as a software engineer at Mozilla, building out our data pipeline and analysis tooling. I’ve been at my current position for more than 10 years (my “anniversary” actually passed while I was out). I started out as a senior engineer in 2011, and was promoted to staff engineer in 2016. In tech-land, this is a really long tenure at a company. I felt like it was time to take a break from my day-to-day, explore some new ideas and concepts, and hopefully expose myself to a broader group of people in my field.

My original thinking was that I would mostly be spending this time building out an interactive computation environment I’ve been working on called Irydium. And I did quite a bit of that. However, I think the main thing I took away from this experience was some insight on what makes a remote environment for knowledge work really “click”. In particular, what makes somewhere feel psychologically safe, and how this feeling allows us to innovate and do our best work.

While the Recurse Center obviously has different goals than an organization that builds and delivers consumer software, I do think there are some things that it does that could be applied to Mozilla (and, likely, many other tech workplaces).

What is the Recurse Center?

Most succinctly, the Recurse Center is a “writer’s retreat for programmers”. It tries to provide an environment conducive to learning and creativity, an opportunity to refine your craft and learn new things, both from the act of programming itself and from interactions with the other like-minded people attending. The Recurse Center admits a wide variety of people, from those who have only been through a coding bootcamp to those who have been in the industry many years, like myself. The main admission criteria, from what I gather, are curiosity and friendliness.

Once admitted, you do a “batch”— either a mini (1 week), half-batch (6 weeks), or a full batch (12 weeks). I did a half-batch.

How does it work (during a global pandemic)?

The Recurse experience used to be entirely in-person, in a space in New York City - if you wanted to go, you needed to move there at least temporarily. Obviously that’s out the window during a Global Pandemic, and all activities are currently happening online. This was actually pretty ideal for me at this point in my life, as it allowed me to participate entirely remotely from my home in Hamilton, Ontario, Canada (near Toronto).

There’s a few elements that make “Virtual RC” tick:

Why does it work?

So far, what I’ve described probably sounds a lot like any remote tech workplace during the pandemic… and it sort of is! In some ways, my schedule and life while at Recurse didn’t feel all that different from my normal day-to-day. Wake up in the morning, drink coffee, meditate, work for roughly 8 hours, done. Qualitatively, however, my experience at Recurse felt unusually productive, and I learned a lot more than I expected to: not just the core stuff related to Irydium, but also unexpected new concepts like CRDTs, product design, and even how visual studio code syntax highlighting works.

What made the difference? Certainly, not having the normal pressures of a workplace helps - but I think there’s more to it than that. The way RC is constructed reinforces a sense of psychological safety which I think is key to learning and growth.

What is psychological safety and why should I care?

Psychological safety is a bit of a hot topic these days and there’s a lot of discussion about in management circles. I think it comes down to a feeling that you can take risks and “put yourself out there” without fear that you’ll be ignored, attacked, or ridiculed.

Why is this important? I would argue, because knowledge work is about building understanding — going from a place of not understanding to understanding. If you’re working on anything at all innovative, there is always an element of the unknown. In my experience, there is virtually always a sense of discomfort and uncertainty that goes along with that. This goes double when you’re working around and with people that you don’t know terribly well (and who might have far more experience than you). Are they going to make fun of you for not knowing a basic concept or for expressing an idea that’s “so wrong I don’t even know where to begin”? Or, just as bad, will you not get any feedback on your work at all?

In reality, except in truly toxic environments, you’ll rarely encounter outright abusive behaviour. But the isolation of remote work can breed similar feelings of disquiet and discomfort over time. My sense, after a year of working “hardcore” remote in COVID times, is that our normal workplace rituals of meetings, “stand ups”, and discussions over Slack don’t provide enough space for a meaningful sense of psychological safety to develop. They’re good enough for measuring progress towards agreed-upon goals but a true sense of belonging depends on less tightly scripted interactions among peers.

How the Recurse environment creates psychological safety

But the environment I described above isn’t that different from a workplace, is it? Speaking from my own experience, my coworkers at Mozilla are all pretty nice people. There’s also many channels for informal discussion at Mozilla, and of course direct messaging is always available (via Slack or Matrix). And yet, I still feel there is a pretty large gap between the two experiences. So what makes the difference? I’d say there were three important aspects of Recurse that really helped here: social rules, gentle prompts, and a closed space.

Social rules

There’s been a lot of discussion about community participation guidelines and standards of behaviour in workplaces. In general, these types of policies target really egregious behaviour like harassment: this is a pretty low bar. They aren’t, in my experience, sufficient to actually create an environment that actually feels safe.

The Recurse Center goes over and above a basic code of conduct, with four simple social rules:

These rules aren’t “commandments” and you’re not meant to feel shame for violating them. The important thing is that by being there, the rules create an environment conducive to learning and growth. You can be reasonably confident that you can bring up a question or discussion point (or respond to one) and it won’t lead to a bad outcome. For example, you can expect not to be made fun of for asking what a UNIX socket is (and if you are, you can tell the person doing so to stop). Rather than there being an unspoken rule that everyone should already know everything about what they are trying to do, there is a spoken rule that states it’s expected that they don’t.

Working on Irydium, there’s an infinite number of ways I can feel incompetent: this is a requirement when engaging with concepts that I still don’t feel completely comfortable with: parsers, compilers, WebAssembly… the list goes on. Knowing that I could talk about what I’m working on (or something I’m interested in) and that the responses I got would be constructive and directed to the project, not the person made all the difference.1

Gentle prompts

The thing I loved the most about Recurse were the gentle prompts to engage with other people, talk about your work, and get help. A few that I really enjoyed during my time there:

… and I could go on. What’s important are not the specific activities, but their end effect of building connectedness, creating opportunities for serendipitous collaboration and interaction (more than one discussion group came out of someone’s checkin post on Zulip) and generally creating an environment well-suited to learning.

A (semi) closed space

One of the things that makes the gentle prompts above “work” is that you have some idea of who you’re going to be interacting with. Having some predictability about who’s going to see what you post and engage with you (that they were vetted by RC’s interview process and are committed to the above-mentioned social rules) gives you some confidence to be vulnerable and share things that you might be reluctant to otherwise.

Those who have known me for a while will probably see the above as being a bit of departure from what I normally preach: throughout my tenure at Mozilla, I’ve constantly pushed the people I’ve worked with to do more work in public. In the case of a product like Firefox, which touches so many people, I think open and transparent practices are absolutely essential to building trust, creating opportunity, and ensuring that our software reflects a diversity of views. I applied the same philosophy to Irydium’s development while I was at the Recurse Center: I set up a public Matrix channel to discuss the project, published all my work on GitHub, and was quite chatty about what I was working on, both in this blog and on Twitter.

The key, I think, is being deliberate about what approach you take when: there is a place for both public and private conversations about what we work on. I’m strongly in favour of open design documents, community calls, public bug trackers and open source in general. But I think it’s also pretty ok to have smaller spaces for learning, personal development, and question asking. I know I strongly appreciated having a smaller group of people that I could talk to about ideas that were not yet fully formed: you can always bring them out into the open later. The psychological risk of working in public can be mitigated by the psychological safety that can be developed within an intentional community.

Bringing it back

Returning to my job, I wondered if it might be possible to bring some of what I described above back to Mozilla? Obviously not everything would be directly transferable: Mozilla has its own mission and goals, and there are pressures that exist in a workplace that do not exist in an environment purely directed at learning. Still, I suspected that there was something we could do here. And that it would be worth doing, not just to improve the felt experience of the people here (though that would be reason enough) but also to get more feedback on our work and create more opportunities for collaboration and innovation.

I felt like trying to do something inside our particular organization (Data Engineering and Data Science) would be the most tractable initial step. I talked a bit about my experience with Will Kahn-Green (who has been at Mozilla around the same length of time as I have) and we came up with what we called the “Data Neighbourhood” project: a set of grassroots micro-initiatives to increase our connectedness as a group. As an organization directed primarily at serving other parts of Mozilla, most of our team’s communication is directed outward. It’s often hard to know what everyone else is up to, where they’re struggling, and how we could help each other out. Attacking that problem directly seemed like the best place to start.

The first experiment we tried was a “data checkins” channel on Slack, a place for people to talk informally about their work (or life!). I explicitly set it up with a similar set of social rules as outlined above and tried to emphasize that it was a place to talk about how things are going, rather than a place to report status to your manager. After a somewhat slow start (the initial posts were from Will, myself, and a few other people from Data Engineering who had been around for a long time) we’re beginning to see engagement from others, including some newer people I hadn’t interacted with much before. There’s also been a few useful threads of conversations across different sub-teams (for example, a discussion on how we identify distinct versions of Firefox for iOS) that likely would not have happened without the channel.

Since then, others have tried a few other things in the same vein (an adhoc coffee chat pairing bot, a “writing help” channel) and there are some signs of success. There’s clearly an appetite for new and better ways for us to relate to each other about the work we’re doing, and I’m excited to see how these ideas evolve over time.

I suspect there are limits to how psychologically safe a workplace can ever feel (and some of that is probably outside of any individual’s control). There are dynamics in a workplace which make applying some of Recurse’s practices difficult. In particular, a posture of “not knowing things is o.k.” may not apply perfectly to a workplace where people are hired (and promoted) based on perceived competence and expertise. Still, I think it’s worth investigating what might be possible within the constraints of the system we’re in. There are big potential benefits, for our creative output and our well-being.

Many thanks to Jenny Zhang, Kathleen Beckett, Joe Trellick, Taylor Phebillo and Vaibhav Sagar, and Will Kahn-Greene for reviewing earlier drafts of this post

  1. This is generally considered best practice inside workplaces as well. For example, see Google’s guide on how to write code review comments

Python dependency gotchas: always go to the source

Aug 16th, 2021

Mozilla Python

Getting back into the swing of things at Mozilla after my extended break. I’m currently working on enhancing and extending Looker support for Glean-based applications, which eventually led me back to working on bigquery-etl, our framework for creating derived datasets in our data lake.

I spent some time working on improving the initial developer experience of bigquery-etl early this year, so I figured it would be no problem to get going again despite an extended hiatus from it (I think it’s probably been ~2–3 months since I last touched it). Unfortunately the first thing I got after creating a fresh virtual environment (to pick up the new dependency updates) was this exciting looking error:

wlach@antwerp bigquery-etl % ./bqetl --help
Traceback (most recent call last):
  File "/Users/wlach/src/bigquery-etl/venv/lib/python3.9/site-packages/google/cloud/bigquery_v2/types/", line 16, in <module>
    from .encryption_config import EncryptionConfiguration
  File "/Users/wlach/src/bigquery-etl/venv/lib/python3.9/site-packages/google/cloud/bigquery_v2/types/", line 26, in <module>
    class EncryptionConfiguration(proto.Message):
  File "/Users/wlach/src/bigquery-etl/venv/lib/python3.9/site-packages/proto/", line 200, in __new__
    file_info = _file_info._FileInfo.maybe_add_descriptor(filename, package)
  File "/Users/wlach/src/bigquery-etl/venv/lib/python3.9/site-packages/proto/", line 42, in maybe_add_descriptor
TypeError: descriptor to field '' doesn't apply to 'FileDescriptorProto' object

What I did

Since we have pretty decent continuous integration at Mozilla, when I see an error like this I am usually pretty sure it’s some kind of strange interaction between my local development environment and whatever dependencies we’ve specified for the repository in question. Usually these problems are pretty easy to solve.

First thing I tried was to type the error into Google, to see if this had come up for anyone else before. I tried several variations of TypeError: descriptor to field and FileDescriptorProto and nothing really turned up. This strategy almost always turns up something. When it doesn’t it usually indicates that something pretty strange is happening.

To see if this was a strange problem particular to us, I asked on our internal channel but no one had offhand seen or heard of this error either. One of my colleagues (who had a working setup on a Mac, the same environment I was using) suggested I set up pyenv to isolate my development environment, which was a good idea but did not seem to solve the problem: both Python 3.8 and 3.9 installed via pyenv ran into the exact same issue.

After flailing around trying a number of other failed approaches (maybe I need to upgrade the version of virtualenv that we’re using?), I broke down and looked harder at the error itself. It seemed to be some kind of typing error in Google’s protobuf library, which google-cloud-bigquery is calling. If this sort of thing was happening to everyone, we probably would have seen it happening more broadly. So my guess, again, was that it was happening due to an obscure interaction between some variable on my machine and this particular combination of dependencies.

At this point, I systematically went through our set of python dependencies to see what might be the matter. For the most part, I found nothing surprising or suspicious. google-api-core was at the latest version, as was google-cloud-bigquery. However, I did notice that the version of protobuf we were using was a little older (3.15.8 when the latest “official” version on pypi was 3.17.3).

It seemed like a longshot that the problem was there, but it seemed like upgrading the dependency was worth a try just in case. So I bumped the version of protobuf to the latest version in my local checkout (pip install protobuf==3.17.3)…

… and sure enough, after doing so, the problem was fixed and ./bqetl --help started working again:

wlach@antwerp bigquery-etl % ./bqetl --help
Usage: bqetl [OPTIONS] COMMAND [ARGS]...

  CLI tools for working with bigquery-etl.


After doing so, I did up a quick pull request and the problem is now fixed, at least for me.

It’s a bit unfortunate that dependabot (which we have configured for this repository) didn’t send an update for protobuf, which would have fixed this problem earlier.1 It seems like it’s not completely reliable for python packages, for whatever reason: I have also noticed this problem with mozregression.

I suspect (though can’t confirm) that the problem here is a backwards-incompatible change made to either protobuf or one of the packages that uses it. However, the nature of the incompatibility seems subtle: bigquery-etl works fine with the old set of dependencies we run in continuous integration and it appears to only come up in specific circumstances (i.e. mine). Unfortunately, I need to get back to what I was actually planning to work on and don’t have time to unwind the rather set of complex interactions going on here. Maybe later!

What I would have done differently

This kind of illustrates (again) to me that while some shortcuts and heuristics can save a bunch of time and mental effort (Googling things all the time is basically standard practice in the industry at this point), sometimes you really just need to start a little closer at the problem to find a solution. I was hesitant to do this in this case because I’m never sure where those kinds of rabbit holes are going to take me (e.g. I spent several days debugging a bad interaction between Kubernetes and our airflow cluster in late 2019 with not much to show for the effort), but often all it takes is understanding the general shape of the problem to move you to a quick solution.

Other lessons

Here’s a couple of other things this experience reinforced for me (these are more subjective, take them or leave them):

  1. As an aside, the main reason we use dependabot and aggressively update packages like google-api-core is due to a bug in pip

10 years at Mozilla

Jul 12th, 2021

Mozilla Recurse

Yesterday (July 11, 2021) was the 10 year anniversary of starting at the Mozilla Corporation. My life has changed a ton in those years: in that time I ended a marriage, changed the city in which I live two times, and took up religion1. Mozilla has also changed pretty drastically in my time here, especially in the last year.

Yet somehow I’m still at it, for more or less for the same reasons that led me to accept my initial offer to join the A-team.2 The Internet has the immense potential to be a force for individual empowerment and yet more than ever, we see this technology used to consolidate unchecked power, spread misinformation, and generally exploit people. Mozilla is not perfect (no organization is: 10 years anywhere will teach you that), but it’s one of the few remaining counter-forces to these accelerating trends. While I’m currently taking a bit of a break to explore some stuff on my own, I am looking forward to getting back to work on the mission when I return in mid-August.

  1. To the extent that Zen Buddhism is a religion. 

  2. I’ve since moved to Data @ Mozilla 

Mini-sabbatical and introducing Irydium

Jun 23rd, 2021

Mozilla Recurse Irydium

Approaching my 10-year moz-iversary in July, I’ve decided it’s time to take a bit of a mini-sabbatical: I’ll be out (and trying as hard as possible not to check bugmail) from Friday, June 25th until August 9th. During this time, I’ll be doing a batch at the Recurse Centre (something like a writer’s retreat for programmers), exploring some of my interests around data visualization and analysis that don’t quite fit into my role as a Data Engineer here at Mozilla.

In particular, I’m planning to work a bunch on a project tentatively called “Irydium”, which pursues some of the ideas I sketched out last year in my Iodide retrospective and a few more besides. I’ve been steadily working on it in my off hours, but it’s become clear that some of the things I want to pursue would benefit from more dedicated attention and the broader perspective that I’m hoping the Recurse community will be able to provide.

I had meant to write up a proper blog post to announce the project before I left, but it looks like I’m pretty much out of time. Instead, I’ll just offer up the examples on the newly-minted and invite people to contact me if any of the ideas on the site sounds interesting. I’m hoping to blog a whole bunch while I’m there, but probably not under the Mozilla tag. Feel free to add to your RSS feed if you want to follow what I’m up to!

Glean Dictionary updates

Jun 2nd, 2021

Mozilla Glean

(this is a cross-post from the data blog)

Lots of progress on the Glean Dictionary since I made the initial release announcement a couple of months ago. For those coming in late, the Glean Dictionary is intended to be a data dictionary for applications built using the Glean SDK and Glean.js. This currently includes Firefox for Android and Firefox iOS, as well as newer initiatives like Rally. Desktop Firefox will use Glean in the future, see Firefox on Glean (FoG).

Production URL

We’re in production! You can now access the Glean Dictionary at The old protosaur-based URL will redirect.

Glean Dictionary + Looker = ❤️

At the end of last year, Mozilla chose Looker as our internal business intelligence tool. Frank Bertsch, Daniel Thorn, Anthony Miyaguchi and others have been building out first class support for Glean applications inside this platform, and we’re starting to see these efforts bear fruit. Looker’s explores are far easier to use for basic data questions, opening up data based inquiry to a much larger cross section of Mozilla.

I recorded a quick example of this integration here:

Note that Looker access is restricted to Mozilla employees and NDA’d volunteers. Stay tuned for more public data to be indexed inside the Glean Dictionary in the future.

Glean annotations!

I did up the first cut of a GitHub-based system for adding annotations to metrics — acting as a knowledge base for things data scientists and others have discovered about Glean Telemetry in the field. This can be invaluable when doing new analysis. A good example of this is the annotation added for the opened as default browser metric for Firefox for iOS, which has several gotchas:

Many thanks to Krupa Raj and Leif Oines for producing the requirements which led up to this implementation, as well as their evangelism of this work more generally inside Mozilla. Last month, Leif and I did a presentation about this at Data Club, which has been syndicated onto YouTube:

Since then, we’ve had a very successful working session with some people Data Science and have started to fill out an initial set of annotations. You can see the progress in the glean-annotations repository.

Other Improvements

Lots more miscellaneous improvements and fixes have gone into the Glean Dictionary in the last several months: see our releases for a full list. One thing that irrationally pleases me are the new labels Linh Nguyen added last week: colorful and lively, they make it easy to see when a Glean Metric is coming from a library:

Future work

The Glean Dictionary is just getting started! In the next couple of weeks, we’re hoping to:

If you’re interested in getting involved, join us! The Glean Dictionary is developed in the open using cutting edge front-end technologies like Svelte. Our conviction is that being transparent about the data Mozilla collects helps us build trust with our users and the community. We’re a friendly group and hang out on the #glean-dictionary channel on Matrix.

mozregression update May 2021

May 10th, 2021

Mozilla Glean Telemetry mozregression

Just wanted to give some quick updates on the state of mozregression.

Anti-virus false positives

One of the persistent issues with mozregression is that it seems to be persistently detected as a virus by many popular anti-virus scanners. The causes for this are somewhat complex, but at root the problem is that mozregression requires fairly broad permissions to do the things it needs to do (install and run copies of Firefox) and thus its behavior is hard to distinguish from a piece of software doing something malicious.

Recently there have been a number of mitigations which seem to be improving this situation:

It’s tempting to lament the fact that this is happening, but in a way I can understand it’s hard to reliably detect what kind of software is legitimate and what isn’t. I take the responsibility for distributing this kind of software seriously, and have pretty strict limits on who has access to the mozregression GitHub repository and what pull requests I’ll merge.

CI ported to GitHub Actions

Due to changes in Travis’s policies, we needed to migrate continuous integration for mozregression to GitHub actions. You can see the gory details in bug 1686039. One possibly interesting wrinkle to others: due to Mozilla’s security policy, we can’t use (most) external actions inside our GitHub repository. I thus rewrote the logic for uploading a mozregression release to GitHub for MacOS and Linux GUI builds (Windows builds are still happening via AppVeyor for now) from scratch. Feel free to check the above out if you have a similar need.

MacOS Big Sur

As of version 4.0.17, the mozregression GUI now works on MacOS Big Sur. It is safe to ask community members to install and use it on this platform (though note the caveats due to the bundle being unsigned).

Usage Dashboard

Fulfilling a promise I implied last year, I created a public dataset for mozregression and created an dashboard tracking mozregression use using Observable. There are a few interesting insights and trends there that can be gleaned from our telemetry. I’d be curious if the community can find any more!

Blog moving back to

Mar 21st, 2021

Mozilla meta

House keeping news: I’m moving this blog back to the domain from This domain sorta kinda worked before (I set up a netlify deploy a couple years ago), but the software used to generate this blog referenced github all over the place in its output, so it didn’t really work as you’d expect. Anyway, this will be the last entry published on my plan is to turn that domain into a set of redirects in the future.

I don’t know how many of you are out there who still use RSS, but if you do, please update your feeds. I have filed a bug to update my Planet Mozilla entry, so hopefully the change there will be seamless.

Why? Recent events have made me not want to tie my public web presence to a particular company (especially a larger one, like Microsoft). I don’t have any immediate plans to move this blog off of github, but this gives me that option in the future. For those wondering, the original rationale for moving to github is in this post. Looking back, the idea of moving away from a VPS and WordPress made sense, the move away from my own domain less so. I think it may have been harder to set up static hosting (esp. with HTTPS) at that time… or I might have just been ignorant.

In related news, I decided to reactivate my twitter account: you can once again find me there as @wrlach (my old username got taken in my absence). I’m not totally thrilled about this (I basically stand by what I wrote a few years ago, except maybe the concession I made to Facebook being “ok”), but Twitter seems to be where my industry peers are. As someone who doesn’t have a large organic following, I’ve come to really value forums where I can share my work. That said, I’m going to be very selective about what I engage with on that site: I appreciate your understanding.