Rated 5 out of 5 stars

It dose help do:
http://lifehacker.com/355973/make-your-extensions-work-with-the-firefox-3-beta

# Type "about:config" into Firefox's address bar and click the "I'll be careful, I promise!" button.
# Right-click anywhere. Choose New>Boolean. Make the name of your new config value "extensions.checkCompatibility" and set it to "false".
# Make another new boolean pair called "extensions.checkUpdateSecurity" and set the value to "false".
# Restart Firefox.

This review is for a previous version of the add-on (1.4.2).  This user has other reviews of this add-on.