Following the Mozilla Foundation-initiated Firefox transition to four-channel development with the release of
Firefox 5 alpha 2 and
Firefox 6 alpha 1 , the Fennec browser (codename for the versions of Firefox Mobile in development) was brought up. Thus, Fennec Aurora and Fennec Nightly became available as successors of Firefox Mobile 4, and Fennec Beta will appear in the future.

Currently, the Fennec Aurora branch contains the code for Firefox Mobile 5, and Fennec Nightly for Firefox Mobile 6, and by the time Firefox 5 is ready to switch to the Beta channel (that is, after a few weeks), Firefox will come to the Nightly place Mobile 7.
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Test versions of Firefox Mobile for Android on ARMv7 (ARMv6 is no longer supported) (in English):
Download .apk Fennec 5.0 alpha 2 Aurora (11.8 MB)
Download .apk Fennec 6.0 alpha 1 Nightly (13.8 MB)
For those who prefer to develop under Firefox Mobile on the desktop and other platforms, the corresponding versions are available on FTP Mozilla.org.
mozilla-central / Fennec Nightly (Firefox Mobile 6.0 alpha 1)ZIP archive for Windows x84 (11 MB)
tar / bz2 archive for Linux i686 (11 MB)
DMG for OS X (18 MB)
DEB-package for Maemo 5 on Qt (14 MB)
DEB package for Maemo 5 on GTK (14 MB)
mozilla-aurora / Fennec Nightly (Firefox Mobile 6.0 alpha 1)ZIP archive for Windows x84 (11 MB)
tar / bz2 archive for Linux i686 (11 MB)
DMG for OS X (18 MB)
DEB-package for Maemo 5 on Qt (13 MB)
DEB package for Maemo 5 on GTK (13 MB)
PS Adobe Flash Player is still not working in any of the editions of Firefox Mobile, this is known, and Mozilla is trying to solve this problem as soon as possible.
PPS If someone from Mozilla Russia reads this, please recommend to your Firefox Mobile colleagues to post all three additional Fennec branches in the Android Market, possibly removing the browser update function through its menu. It will be more organic to integrate Firefox into the Android ecosystem, rather than constant referrals to the Mercurial repository.