The nightly builds still reflect the early-days pre-alpha version of Fennec like the one we test-drove in April. Needless to say, these builds are targeting dedicated testers and bug-hunters who don't mind rebooting their phones when instability strikes.
If you'??ve got an Android phone running version 2.0 of the operating system or higher, you'??ll need to uninstall previous builds of Fennec before downloading the latest. Manual uninstallation and reinstallation will be temporary, however. Auto-updating will come to Android developers and testers eventually.