Firefox/TBird freezes

Freezes happen randomly since loading latest version 3 days ago. It will definitely freeze if left on and alone for a while. Other times it takes as long as reading an article. Happens when FF is on and TBird not launched or launched. TBird also freezes since 3 day ago loaded latest version. Nothing else has been loaded and a thorough deep virus scan has been done.
Love some help on this and/or would like to know if there is a location for downloading previous versions (no problems with either) and installing previous versions of both FF and TBird. I would prefer to work on solving the problem but need some direction.