Firefox Snap Packaging

This page explains interactions between Firefox and Snap packaging format.

Where is the upstream

The code reference itself is mozilla-central, but the packaging is being worked within the Canonical’s firefox-snap repository.

This packaging includes a few more bits and dependencies, including compiler. It will also re-download the mercurial repository: this is on purpose.

Where to report bugs

All bugs should be reported to Bugzilla’s Third Party Packaging component, and marked as blocking snap meta-bug.

Build process

While there is an existing repackage task, is currently is no up-to-date and it is not usable from mach (work is being tracked in for this), so unfortunately the only way to work right now is a full rebuild using upstream tooling.

The following steps should be enough, assuming you have properly setup:

While the documentation still refers to Multipass, the Firefox Snap and its dependency had some requirements that made it better suited to use LXD.

When performing the checkout, please keep in mind the branch mapping:

  • edge is our nightly

  • beta is our beta

  • stable is our release

  • esr is our esr

$ git clone --branch BRANCH
$ snap run snapcraft

You should end up after some time with two files: firefox-XXX.snap and firefox-XXX.debug. The first one is the package you will want to snap install while the second one holds your debugging symbols.

You can then install the package:

$ sudo snap install --name firefox --dangerous ./path/to/firefox-XXX.snap

If you want to have parallel installs, then you can change the –name firefox to something else. This will be the name you use for snap run installed-name, e.g., --name firefox_nightly will require you to run snap run firefox_nightly.

Snap has a notion of plugs and slots, and some gets automatically connected in various ways, including depending on the Snap Sore itself, and if you manually install as firefox it should reuse them (but you might do bad things with your profile). If you install using another name, then the Snap Store automatic connection will not happen and this can result in a broken state. Inspecting snap connections firefox using a store-installed snap should get your an accurate list that you can replicate.

What CI coverage

Currently, there are upstream-like builds on treeherder. They are scheduled as a cron task daily and includes:

  • building opt/debug versions of the snap

  • building them on all branches

  • running a few selenium-based tests

The build definitions are based on docker.

It should be noted that for the moment, all tasks needs to run under docker. However, this setup is not working for Snap since it interacts with SystemD which does not work under Docker. This is why the installation is handled by the install-snap script rather than plain sudo snap install, and also why we need to run snap in destructive mode (which is fine since we are within a docker container). This does not apply to the tests case which relies on newly-available wayland virtual machines.

Outside the build oddities because of the setup, it should be noted that those builds are as close as possible to upstream. This means:

  • the mozilla-central hash they run against is not matching the source code it builds from, and one should inspect the build log to see the mercurial clone step

  • it builds using the clang build within the snap definition

The tests are defined within the docker subdirectory. They are using Selenium because this is what was used by pre-existing tests ran on GitHub Actions from upstream.

Their coverage is ensuring that we get a basic working browser out of builds. It includes some tests that previously were manually ran by QA.

How to hack on try

Build and test tasks can be explored via mach try fuzzy --full by searching for 'snap 'upstream. There is a bit of hacking for try to make sure we actually don’t re-download the mercurial repo and directly reuse the clone generated by run-task, handled in the script.

So pushing to try is basically just:

$ mach try fuzzy --full -q "'snap 'upstream 'try"

Because of the build process, a full opt build will take around 1h45-2h while a debug build will be around 60 minutes, the difference coming from the use of PGO on opt builds.

If you need to reuse a package from the Snap Store or from the latest mozilla-central or a specific successful build, you can use USE_SNAP_FROM_STORE_OR_MC en variable ; setting it to store will download from the Snap Store (warning: no debug builds on the Snap Store, so whatever debug variants we have will be an opt build in fact), and setting to a TaskCluster index value will download from the index. Set it to latest if you want latest, or explore the TaskCluster index for others. Any try will be pulled from latest nightly while others will be fetched from their respective branches.