I'm assuming you have a new C2D Macbook Pro, like me.
Move the three Flash files out of /Library/Internet Plug-ins and into your own ~/Library/Internet Plug-ins folder. It shouldn't matter, but it does (I was pulling my hair out over this until I chanced upon the solution while trying to debug the problem!).
I suspect it's because "Flash Player Enabler.plugin" is still a PPC app, while the other two files are Universal.
The three files are:
Flash Player Enabler.plugin
Flash Player.plugin
flashplayer.xpt
Since you have a workaround, I was wondering if the problem or the workaround has been reported to Adobe. Even if it's a comment at VersionTracker or MacUpdate, even that would help.
Hmm... looks like their solution is easier. You can supposedly just delete the pluginsreg.dat file (from your ~/Library/Application Support/Firefox folder) while Firefox is not running.
Also looks like it's only a problem for those of us who tried migrating our profiles over from a PPC mac to an Intel mac.
So, once again, saving your bookmarks file and killing the profile saves the day. Sad that data corruption has caused so many problems for so many people.
Yeah, I've done that in the past too with Firefox and with Thunderbird. But now, with things like cookies and ads being selectively blocked, my junk mail filter being pretty well trained, etc. I hate to lose all my settings (some of which aren't in flat text files unfortunately).
Tried all above without any luck. This worked for me:
-Backup profile bookmarks somewhere:
-Backup anything else in your profile you'd like to keep.
-Close Firefox
-Remove everything in ~/Library/Application Support/Firefox
-Restart
Removing a profile for nothing can be painful so check
with a fresh user that this will work for you.