I'm running Firefox 3.6.13 on Windows 7 and I've just started getting the same script error when I'm on webpages, particularly Livejournal ones. The script error is js/ff_browser:28
I was prompted to change my display settings but this has had no effect either - I still get the message.
I have no idea why it's just started - I haven't downloaded any new software or deleted any recently that I think would have any connection to Firefox.
I am running Firefox 9.0.1 and it has crashed several times since loading. Some were due to the AVG Security Toolbar but that is now disabled.