oh uh try
close firefox.
go to your 
profile directory  find your "extensions.rdf"  file and rename it to "extensions.old.rdf"
restart firefox.

 tell me if that fixes it
quote:
Originally posted by Reaper
that might be the problem, the extension might not be supported in the beta version. try downgrading to version 1.07 and see what happens 
no , ive had this happen in everything > 1.0  and downgrading wont solve it , before 1.5 i used to just create a new profile but now extensions are handled differently so deleting /renaming the extensions.rdf normally fixes such problems