firefox hangs to much how do I reinstall a previous version tha worked

I installed the updated version of firefox. Since then whatever page I'm on freezes for about 1-2 mins. I have uninstalled & reinstalled firefox & java script cleaned out everything else cookies etc & still firefox hangs..... I've tried looking for the version I had before but cannot get it. So how can you help me solve the problem..... every ten mins or so it hangs