|You need to remove any trace of FF|
I had problems with add blocker extension for firefox v1.0.4. I had to uninstall firefox in add/remove programs.
Next I had right click on start, explore>Tools>Folder Options>View>Show hidden files and folders. Make sure it is checked.
You'll need to delete your profile.
On Windows XP/2000 it's C:\Documents and Settings\[user name]\application data\
Delete the "Mozilla" folder unless you use Netscape 6/7 or the Mozilla Suite (if you do, delete the Firefox folder)
Now re-install FF
Here is how I stumbled on to this:
Here is the FF help forum:
P.S. I'm going to be extra careful checking version conflicts with extensions for FF. I've read that you should always go to add and remove programs to install a new version of FF. If you update version of FF in FF supposedly it isn't as good. All your settings will be save automaticallly unless you delete your profile as stated in the beginning of this post.