Classic Logic

Mozilla 101

It’s been a while since I’ve started contributing code to the Mozilla codebase.

Because I frequently nuke and re-install everything on my primary computer (due to other experiments that have nothing to do with Mozilla), I’ve decided to write myself a reference I can quickly refer to when setting up the local version of Firefox. All of the following were performed on Debian-based distros.

I plan to make this a living document; expect changes here as I learn more.

None of this is official. I’m just documenting what worked for me.

1. Firefox

1.1 Initial Build

Build instructions on Linux machines are here. It goes something like this:

mkdir src && cd src
wget https://hg.mozilla.org/mozilla-central/raw-file/default/python/mozboot/bin/bootstrap.py
python2 bootstrap.py

Apparently, bootstrap.py only works with python 2 (the last time I checked). On my machines, python defaults to python 3, and hence the python2 above to be on the safer side. Follow the prompts and stick with the defaults. Accept anything that claims to make your life easier (such as the several widgets and tools). Whatever you do, ensure that mozreview is set up correctly.

I normally don’t allow bootstrap.py to clone mozilla-unified, and instead clone mozilla-central repository.

hg clone https://hg.mozilla.org/mozilla-central

You now have all the code available locally. Now it’s time to build Firefox:

cd mozilla-central
./mach build
./mach run

The build can take a while. The last command above runs firefox once the build is complete.

1.2 Updating Local Copy

Must do this when you’re about to start working on a new bug.

hg pull
hg update central
./mach build

While attempting to build, it sometimes complains that a clobber is required, along with instructions on how to do that. Follow the instructions. If clobber is not required, then builds tend to be faster.

1.3 Submitting Code For Review

(These are simple instructions for those who have already read the official documentation).

Mozilla has moved away from mozreview in the recent past. The recommended way for code review is now via Phabricator.

Before you do anything, ensure you have an account with Mozilla’s Phabricator instance.

You need to install:

  1. Arcanist – installation instructions are in the Arcanist Quick Start guide and in here. Required for moz-phab (next step).
  2. moz-phab

Once all that is set up, to submit a commit for review, do

moz-phab submit

moz-phab should do the rest; you might want to verify that your submission appears in Phabricator.

2. Taskcluster

Components like Taskcluster don’t come along with Firefox. This should have been obvious, but it took me an hour to get this.

Taskcluster is hosted on GitHub (link below), and according to this official page, fork and clone the necessary repo to hack on Taskcluster (and make a pull-request once you’re done). For instance to work on taskcluster-queue:

git clone https://github.com/taskcluster/taskcluster-queue.git

You need to install yarn before you can, say, run tests on certain files. The official instructions for installing yarn goes something like the follows:

curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -
echo "deb https://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.list
sudo apt update && sudo apt install yarn

To install the dependencies in a project (such as eslint maybe):

yarn install

To run all tests:

yarn test

To run a specific test:

$(npm bin)/mocha ./path/to/file.js

Some test results might show its results as “Pending”. According to Dustin J. Mitchell, “‘Pending’ means that the tests are skipped because the necessary credentials are not available.”

There are also some things involving credentials you need to be aware of. To be honest I don’t fully understand this bit yet. And for certain features you need to use Taskcluster CLI:

wget https://index.taskcluster.net/v1/task/project.taskcluster.taskcluster-cli.latest/artifacts/public/linux-amd64/taskcluster
chmod +x taskcluster
./taskcluster help

You can replace “help” above with other commands, such as “signin”.