Maybe some important file got corrupted. Try doing:

~$ killall -9 browser
~$ mv .mozilla temp.mozilla

repeat for:

.bookmarks
.browser
.browser_typed_urls

(become temp.bookmarks etc.)

Then start the browser, and see if it works. If this didn't help, move the directories back with the same commands with names in reverse. Edit: if you want to move them back and it's already created new ones, remove the new ones first using rm -r dir.