Rated 4 out of 5 stars

Temp Fix for FF4
Go to Windows Explorer and type %appdata% to locate your application data folder.
Browse Mozilla > Firefox > Profiles > ... > extensions > toggleprivatebrowsing@supernova00.biz

Open install.rdf and overwrite the maxVersion by
"<em:maxVersion>4.0</em:maxVersion>" and save.
Relaunch FireFox
Click on Toolbar, Customize, Drag and drop the "Infinity" button (Toggle Private Browsing)