Firefox for Android

Our release team submits Beta and final release builds to the Android market, not sure if there are any plans to go for the F-Droid repo as well. We also have APKs available that can be installed directly from our website and receive updates through our own update check mechanism.
There's new Aurora and Nightly builds every day, I'm not sure how well that works with any market or repo, so I think http://www.mozilla.org/en-US/firefox/channel/#aurora/auro... and http://nightly.mozilla.org/ are probably the better variants to get them. Note that those builds are still heavily under development.