Sounds like all the files and what not were still saved when you reinstalled it again to try and fix it.
I'd recommend..
Uninstall Firefox again.
Then go into its folder. C:\Program Files\Mozilla Firefox
Delete the whole folder.
Download a registry cleaner from
www.download.com . Search for "registry cleaner" and find a free one for the moment.
Run the cleaner, if you have time. Once done, restart your computer.
Try reinstalling Firefox again.
Also, what I remember was that when you uninstall firefox, it asks if you want to save your profile or something.. (if it's not firefox, then igonore it.) If so.. say no.