I am using Ubuntu 8.04 and Firefox version on a 64bit AMD machine.

Please refer to this thread

There is a profile directory in /usr/lib/firefox/defaults/profile that i have tried to delete and restart firefox.

I also tried to reinstall firefox 2.

I am unable to install any extensions, foxmarks in particular. It use to work fine on 7.1 though.

This is the error I get:

Error: installLocation has no properties
Source File: file:///usr/lib/firefox/components/nsExtensionManager.js
Line: 3938