If some Firefox extension or add on started giving you trouble, and the trouble is so serious that Firefox simply fail to start, then what to do? Here is the simple way you can uninstall any Firefox extension:
Go to User’s - $Documents and Settings\a\Application Data\Mozilla\Firefox\Profiles\
directory (the example is for user a under Windows. In Linux, the folder may be stored in your home directory under hidden directory .mozilla). You will find a cryptic directory such as this - p79bty4k.default. Under this directory, you will find a directory named extensions. Within that directory, all your Firefox extensions that you have installed so far were available. Now choose the offended one among the list – that may be an entry or a sub directory – and delete it. Restart Firefox. The offended firefox extension will vanish forever.