It's a version of Firefox Fennec for the Android phone.
It's a "pre-alpha" release, announced by Mozilla developer Vladimir Vukicevic on his personal blog. He gave a link from which you can download the current build.
It's not for grandma, or for casual walking around, he writes. Some of the limitations:
Most of this stuff will be fixed as the developers go along. Vukicevic calls it "a pre-nightly build (even earlier than pre-alpha)." Don't say you weren't warned.
But still. Wa-ha-ha-ha. Candid software. Nudge, nudge. If you're a man of the world, squire, you might like to give it a tumble. One of the best contributions you can make to open source, as a non-programmer, is to try out new code.