The team working on the new Australis version of Firefox (myself included) is starting to get close to merging to mozilla-central. We’re too far from being able to say exactly when this code will merge, but I want to go over our backout plan for Australis.

As you may or may not know, Australis is a project to provide an updated visual design, streamlined tab strip, new Firefox menu and improved customization capabilities.

Due to its large scope, Australis couldn’t be implemented with the ability to toggle its presence via an about:config preference. This unfortunately carries with it a more burdensome plan to undo the changes should there be issues that lead us to delay the release of Australis.

When Australis (currently located on the UX branch) merges to mozilla-central, the Australis team will manage a special project branch that mirrors mozilla-central but excludes the Australis changes. This branch is located in the temporary Holly project.

In the likely chance that we choose to hold Australis on the Nightly train for an extra release cycle, we will use Holly to merge to mozilla-aurora. This will allow the mozilla-central changes not related to Australis to continue moving along with the release trains.

This also presents an issue in that the code that reaches Aurora will have a tiny fraction of the testing hours on it compared to the Nightly builds. To work around this, I’m asking that users who aren’t interested in Australis use the Holly branch for their Nightly builds. This will help spread out some of the testing hours and make sure to catch any potential merge bustage faster. I’ll be posting a link to download Holly nightlies once we merge from UX to mozilla-central.

In the meantime, if you are looking to help test Australis you can download a build from the UX branch.