Thanks!
You may uninstall Avast Webrep until they get it fixed. This is what I did and Firefox is now working fine on my system (Win7 64x). 
To uninstall Webrep: http://www.technogadge.com/remove-avast-webrep/
I have the same problem with WebRep. It slows down Firefox every time I do a search on Google. Google’s Autocomplete takes a while to load and causes Firefox to hang for a bit. I checked and it made Firefox consume 50% CPU load. It only seems to happen on Google for me. The rest seem fine. I’m glad to find out I’m not the only one having issues with this.
i have the same problem!i uninstalled firefox,put it to default settings,remove add ons,then i notice it’s webrep causing the problem…google chrome doesn’t have the problem…only firefox in my situation and it keeps crashing facebook!
I’ve disabled webrep and no problems. Facebook was like trawling through treacle with it on.
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