There could be any number of reasons why it works on one of your computers and not the other... that's not really a useful road to go down since it's the laptop that's having the problem and not your desktop or any laptop or desktop anywhere else that's not having problems.

I think it would be worthwhile to try a slightly older version of Firefox to see if it's a bug in the latest one. Also, according to some info I got in another thread
there was a recent issue with Flash and Firefox, which prompted the release of FF13.0.1 and Flash 11.3.300.262.
So it's not beyond the realm of possibilities this could be somehow related.

Try one of the Version 10 FF's here.. http://www.oldapps.com/firefox.php

It will install over top of the existing version the same way as a newer version will.