Above, I kept on mentioning how a Google search soon brings up loads of threads about this issue.
This article in particular really describes the problem in detail:
http://robertlindsay.blogspot.com/20...x-cpu-bug.html
....and lays the blame at the closed source Flash player, although admits Firefox has some issues itself. Since users of other browsers have reported similar issues, I tend to agree that Flash really needs to sort out its non-ActiveX plugin.