was getting Security error code: 1000 being thrown by FF (2.0.0.3/mac) in my firebug console. In the FF error console, i would get this (which helped a bit more) Error: uncaught exception: [Exception... "Security error" code: "1000" nsresult: "0x805303e8 (NS_ERROR_DOM_SECURITY_ERR)" location: "path_to_script/_javascript/swfobject_source.js Line: 190"]
Same page was working fine in safari.
Jumping to line 190 i really couldn't tell what was causing the security error. I can tell what the function is for [thats straight-forward enough from the code-comment), but not what could be the source of the error. Anyhow, just having that function return ""; got it working again.
I know I've probably broken some sort of functionality, but it seems to be working for our needs.
Just posting in the hopes that a) this helps someone else stuck like me, and b) that this can be fixed, or worked around properly, without losing any functionality.
There was another post a short time ago which concluded that the Firebug extension actually causes some errors which don't appear without it installed. Try temporarily uninstalling the extension, and see if you still get any js errors.
I can duplicate it, but it may be a different scenario. I had the -exact- same error in Firefox 2.0.0.6 today. I was doing data validation in a submission form, and one of the things I do is strip leading and trailing whitespace from form fields.
Turns out that if you modify an <input type="file"> element's contents, it throws this error as a security error. This is sensible, since if you were allowed to arbitrarily alter the contents of said widget, you could basically request any file from the user's hard drive that you wanted.