Vicki and I both upgraded to Firefox 1.5 (on Mac OS X) in the last couple of weeks. Vicki went first, and she had a problem with something that went away when she uninstalled all the extensions she uses and reinstalled them. Then after a short time she found it was so unstable that she switched to Safari. Then I noticed that I couldn’t get Flash to work on any site. I tried uninstalling FlashBlock, and that didn’t help. I tried upgrading to Flash 8, and that didn’t help. Eventually I discovered that if I go into my profiles directory (in ~/Library/Application Support/Firefox/Profiles/foo) and deleted all the extensions related files and directories, Flash worked again. I installed FlashBlock and the Google Toolbar, but I can’t seem to find the BugMeNot extension. Oh well, I guess I’ll have to do that the old fashioned way.
But it seems like Firefox really screwed up when it comes to upgrading when you have extensions installed.