Firefox has recently become unbelievably slow and laggy

Since a few months back, Firefox has become incredibly slow and laggy. To open a website (any website really, even Wikipedia) seems to be such a burden for it. If I play a Youtube clip it will frequently stop it when loading a new site.



How to fix this? I tried SpeedyFox, but it only fixes the problem for a few hours, or a day at most. Any other way to fix it? A more permanent way?

via JREF Forum http://ift.tt/1l5vrSH