That might be true in your case, but I'm running Firefox 21 smoothly with over 11 tabs open as I type this. And I have a truckload of addons changing my addon b

That might be true in your case, but I'm running Firefox 21 smoothly with over 11 tabs open as I type this. And I have a truckload of addons changing my addon bar approximately 12(of 24 installed). What you are experiencing is definitely abnormal. The only days I have that kind of performance issue is on my old laptop. In which case try switching to Aurora/Nightly, it might help.