This really isn’t Systems Administration related, but I recently started using a tool called blogjet to write blog entries and had a hard of a time getting the extensions to work properly in Firefox. It was telling me that the BlogJetThis! extension was not compatible with Firefox 3.0.6.
Essentially, It looks like it was installing a Firefox 2 extension… even though the extension said it was for “< 2.0”. A quick google search found this article that solved the issue.