Releasing geckodriver

Releasing geckodriver is not as easy as it once used to be when the project’s canonical home was on GitHub. Today geckodriver is hosted in mozilla-central, and whilst we do want to make future releases from Mozilla’s CI infrastructure, we are currently in between two worlds: development happens in m-c, but releases continue to be made from GitHub using Travis.

The reason for this is that we do not compile geckodriver for all our target platforms, that Rust cross-compilation on TaskCluster builders is somewhat broken, and that tests are not run in automation. We intend to fix all these problems.

In any case, the steps to release geckodriver are as follows:

Release new in-tree dependency crates

geckodriver depends on a number of Rust crates that also live in central by using relative paths:

mozprofile = { path = "../mozbase/rust/mozprofile" }
mozrunner = { path = "../mozbase/rust/mozrunner" }
mozversion = { path = "../mozbase/rust/mozversion" }
webdriver = { path = "../webdriver" }

Because we need to export the geckodriver source code to the old GitHub repository when we release, we first need to publish these crates if they have had any changes in the interim since the last release. If they have receieved no changes, you can skip them:

  • testing/mozbase/rust/mozprofile
  • testing/mozbase/rust/mozrunner
  • testing/mozbase/rust/mozversion
  • testing/webdriver

For each crate:

  1. Bump the version number in Cargo.toml
  2. cargo publish

Update the change log

Notable changes to geckodriver are mentioned in Many users rely on this, so it’s important that you make it relevant to end-users. For example, we only mention changes that are visible to users. The change log is not a complete anthology of commits, as these often will not convey the essence of a change to end-users. If a feature was added but removed before release, there is no reason to list it as a change.

It is good practice to also include relevant information from the [webdriver] and rust-mozrunner crates, since these are the two most important dependencies of geckodriver and a lot of its functionality is implemented there.

We follow the writing style of the existing change log, with one section per version (with a release date), with subsections ‘Added’, ‘Changed’, and ‘Removed’. If the targetted Firefox or Selenium versions have changed, it is good to make a mention of this. Lines are optimally formatted at roughly 72 columns to make the file readable in a text editor as well as rendered HTML. fmt(1) does a splendid job at text formatting.

Update libraries

Make relevant changes to Cargo.toml to upgrade dependencies, then run

% ./mach vendor rust
% ./mach build testing/geckodriver

to pull down and vendor the upgraded libraries. Remember to check in the Cargo.lock file since we want reproducible builds for geckodriver, uninfluenced by dependency variations.

The updates to dependencies should always be made as a separate commit to not confuse reviewers, because vendoring involves checking in a lot of extra code already reviewed downstream.

Bump the version number

Bump the version number in Cargo.toml to the next version. geckodriver follows semantic versioning so it’s a good idea to familiarise yourself wih that before deciding on the version number.

After you’ve changed the version number, run

% ./mach build testing/geckodriver

again to update Cargo.lock, and check in the file.

Export to GitHub

The canonical GitHub repository is

so make sure you have a local clone of that. It has three branches: master which only contains the; old which was the state of the project when it was exported to mozilla-central; and release, from where releases are made.

Before we copy the code over to the GitHub repository we need to check out the commit we made earlier against central that bumped the version number:

% git checkout $BUMP_REVISION


% hg update $BUMP_REVISION

We will now export the contents of testing/geckodriver to the release branch:

% cd $SRC/geckodriver
% git checkout release
% git rm -rf .
% git clean -fxd
% cp -r $SRC/gecko/testing/geckodriver .

Manually change in-tree path dependencies

After the source code has been imported we need to change the dependency information for the mozrunner, mozprofile, mozversion, and webdriver crates. As explained previously geckodriver depends on a relative path in in the mozilla-central repository to build with the latest unreleased source code.

This relative paths do not exist in the GitHub repository and the build will fail unless we change it to the latest crate versions from That version will either be the crate you published earlier, or the latest version available if no changes have been made to it since the last geckodriver release.

Commit local changes

Now commit all the changes you have made locally to the release branch:

% git add .
% git commit -am "import of vX.Y.Z"

As indicated above, the changes you make to this branch will not be upstreamed back into mozilla-central. It is merely used as a staging ground for pushing builds to Travis.

Tag the release

Run the following command to tag the release:

% git tag 'vX.Y.Z'

Make the release

geckodriver is released and automatically uploaded from Travis by pushing a new version tag to the release branch:

% git push
% git push --tags

Update the release description

Copy the raw Markdown source from into the description of the latest release. This will highlight for end-users what changes were made in that particular package when they visit the GitHub downloads section.

Congratulations! You’ve released geckodriver!

Future work

In the future, we intend to sign releases so that they are verifiable.