someone else could probably give you better advice than i can, but i'd make sure firefox and flash/silverlight (whichever you use) are both updated (if you haven't done so already). maybe check which add-ons are running in firefox and disable what's unnecessary, or clear your browser history/cache. even scanning with something like malwarebytes, if you'd like to, wouldn't hurt.
here are some additional tips that might help, and
this amazon article could be useful