I had Firefox suddenly start to behave strangely:

I would see strange looking tabs, and many blank pages, instead of websites… and the occasional “page not found” message.

Yet IE8 was working fine.

I disabled all the plugins, and FF would then start working normally again.

After a bit of trial and error, I eventually found that the problem was with the tab kit plus add-on.

But the add-on was working fine on another similar PC…

So I thought: maybe tab kit plus has some corrupt data, so I’ll uninstall it, restart FF, then re-install tab kit plus.

Well, it didn’t seem to have any effect.

After some research, I found that this can sometimes happen to Firefox, and the only way out, is to create a new profile.

Since creating a new profile, means you will lose all the bookmarks, plugins, etc from the old profile, I made a backup of the bookmarks:

bookmarks -> organise bookmarks -> import and backup -> backup -> select where to save the backup (and its name).

I then shutdown firefox (restart your PC if you want to be sure).

Then from a command prompt (cmd), I enter:

firefox -ProfileManager

The window that pops up allows you to create a new profile (create profile button), and I also delete the old corrupt profile (delete profile button).

I then Exit, and start firefox normally, and I get an “out of the box” firefox.

I then import the favorites, and re-install the plugins, and the problem is gone.

An interesting side effect of this is:

With the new profile, Firefox seems much faster (even with all the add-ons and bookmarks back to normal!)… I wonder if Firefox needs a “cleanup” function / add-on, to maintain its performance?