updated 12:20 pm EDT, Tue March 29, 2011
Firefox 4 Mobile final hits Android
The browser brings HTML5 but notably doesn't include Flash. Performance has so far been cited as the main limitation and should see Adobe's plugin arrive at an undetermined point in the future.
Using the browser on Android needs at least Android 2.0. Most Android phones will work, but Mozilla has specifically excluded the original Motorola Droid and its Milestone equivalent.