Those of us who beat their browsers mercilessly often notice a slowdown in responsiveness and sometimes dysfunctionality. This happens on both Windows and Linux. Many of our users have remarked at how fast their browsers feel after a "cleanup" or a system reload. Firefox can be rejuvenated by the following almost simple procedure:

• create a new user on your system - System, Administration, Users and Groups on Ubuntu. Let's call him "joe" and you "me".
• close all you instances of Firefox
• in you home directory move .mozilla to .mozilla.bak
• cp /home/joe/.mozilla .
• sudo chown -R me.me .mozilla
• restart Firefox

You will have to set up your preferences and bookmarks and all you saved cookies and passwords will be gone but you should have a much more responsive and faithful Firefox as a result.