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.

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

Update in-tree dependency crates

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

mozdevice = { path = "../mozbase/rust/mozdevice" }
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 received no changes, you can skip them:

  • testing/mozbase/rust/mozdevice

  • 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. Update the crate: cargo update -p <crate name>

  3. Commit the changes for the modified Cargo.toml, and Cargo.lock (can be found in the repositories root folder). Use a commit message like Bug XYZ - [rust-<crate name>] Release version <version>.

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, rust-mozrunner, and rust-mozdevice crates, since these are the 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 targeted 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.

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 and update the support page

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

After you’ve changed the version number, run

% ./mach build testing/geckodriver

again to update Cargo.lock.

Now update the support page by adding a new row to the versions table, including the required versions of Selenium, and Firefox.

Finally commit all those changes.

Add the changeset id

To easily allow a release build of geckodriver after cloning the repository, the changeset id for the release has to be added to the change log. Therefore add a final place-holder commit to the patch series, to already get review for.

Once all previous revisions of the patch series have been landed, and got merged to mozilla-central, the changeset id from the merge commit has to picked for finalizing the change log. This specific id is needed because Taskcluster creates the final signed builds based on that merge.

Release new in-tree dependency crates

Make sure to wait until the complete patch series from above has been merged to mozilla-central. Then continue with the following steps.

Before releasing geckodriver all dependency crates as updated earlier have to be released first.

Therefore change into each of the directories for crates with an update and run the following command to publish the crate:

% cargo publish

Note that if a crate has an in-tree dependency make sure to first change the dependency information.

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 release commit that bumped the version number on mozilla-central:



% git checkout $RELEASE_REVISION

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

% cd $SRC/geckodriver
% git checkout release
% git pull
% git rm -rf .
% git clean -fxd
% cp -rt $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 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. It is recommended to setup a GPG key for signing the commit, so that the release commit is marked as verified.

% git add .
% git commit -S -am "import of vX.Y.Z" (signed)

or if you cannot use signing use:

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

Then push the changes:

% git push

As indicated above, the changes you make to this branch will not be upstreamed back into mozilla-central. It is merely used as a place for external consumers to build their own version of geckodriver.

Make the release

geckodriver needs to be manually released on Therefore start to draft a new release, and make the following changes:

  1. Specify the “Tag version”, and select “Release” as target.

  2. Leave the release title empty

  3. Paste the raw Markdown source from into the description field. This will highlight for end-users what changes were made in that particular package when they visit the GitHub downloads section. Make sure to check that all references can be resolved, and if not make sure to add those too.

  4. Find the signed geckodriver archives in the taskcluster index by replacing %changeset% with the full release changeset id. Rename the individual files so the basename looks like ‘geckodriver-v%version%-%platform%’. Upload them all, including the checksum files for both the Linux platforms.

Congratulations! You’ve released geckodriver!