We have just released a new version of the standalone version of ForceField 188.8.131.52 that is now compatible with FireFox 3.5.5
NOTE: Users of Extreme with the built in version of ForceField should not download this because its not compatible with the built in version.
Your update has already been delivered silently in an update that already went out. That update only applies to XP users.
Standalone ForceField users can download the new version from:
This is the small down-loader that will determine the proper version to download and install depending on your OS.