All-In-One-Guestures...
I did this quick hack:
1. Go to %appdata%\Mozilla\Firefox\Profiles\YOUR DEFAULT PROFILE\extensions\{8b86149f-01fb-4842-9dd8-4d7eb02fd055}
2. Edit the install.rdf file there (any text editor will do or XML editor if you want to be fancy).
3. Find the maxVersion element. It is currently set to 3.5- Change this to 4.0
And viola. The only thing I've noticed is the mouse "trails" have disappeared but I'll live with that until the update is posted.