Now, both the desktop and the mobile version will be on Github, and the "issues" will stay on Bugzilla.
This will take advantage of both GitHub's good search and source browsing and Git's familiar system.
As a former Firefox and Thunderbird contributor, I have to say that I used local search instead of trying to find something on the mozilla-central website.
Of course, when you're actively developing software, you search inside your IDE, but allowing to find things easily on the website makes it more welcoming for potential new contributors.