Back in my windows days......

I used to use this
app to clean the registry with problems such as you describe.
In this case,I would first backup my bookmarks.
Then uninstall firefox.
Then search for all instances of the offending application,(firefire/mozilla)then delete them all.
EDIT (Make sure you name your bookmarks backups something without the mozilla/firefox in the name so you don't accidentelt delete it here)
Then use the registry cleaner.Windows isn't going to do it for you.
Re-install the newer version of the app.
The reg cleaner application will tell you which entries are useless deadends.
You can pick and choose which to delete,or choose them all.
If you have never editted your registry,or used an application like this before,be prepared to be very surprised as to how many useless entries there are in the windows registry.
To test this,clean your registry.
Install any application you want just for this test.
Use windows add/remove programs feature,and/or use the un-installer for the application.
All clean right?
Search for any instances of the app you just uninstalled.
How many did you find?
Run the reg cleaner app again.
More useless garbage in the registry.
Windows never gets it right.
Of course you could switch to linux like I did.
