Sorry about that! To help us figure out the problem, can you tell us (if you remember) what you were doing with Firefox before the problem started? In particular, did you switch Firefox to use a different language, or install/remove any add-ons?

You can open the Android "Settings" app and go to the "Applications" section to force Firefox to exit, which might help. If that doesn't work you can use the same Settings page to "clear data" which will probably fix the problem but will erase your settings and bookmarks. (You can then use Firefox Sync to copy your bookmarks from another computer if you want.)

While More info. is needed, I'd reboot and clear my history/cookies. Normally a lock-up has to do with something outside the Firefox executable.