No one's here to criticize browser choices...
I use Opera, and I've been getting flash errors a lot lately. Thought it was fixed with my last Java and Flash player update, but the problem has since come back. I don't get any slowdowns, though. These things usually get fixed rather quickly, because they are annoying, but slowdowns can be worrying.
I suggest you run a few AV scans, F-secure, Avast or Housecall, just to be safe.... This thread shouldn't be in this segment of the forum, though...