I too have terrible problems with Adobe Flash and Firefox but
everything works fine in Opera or Chrome so it's not Flash on the PC
that's the problem but the plugin for Firefox. Even removed Firefox
totally using Synaptic and put back, plus replaced the plugin file -
no dice, Firefox refuses to play flash video :-(

I'm hanging fire on doing any more about it until 12.04LTS is out and
evaluating the switch to it. Having other browsers that work means
it's not such an issue, if mildly annoying