[beagle3]

Maybe it is interaction between it and another addon. I just removed and reinstalled all my addons last week and performance was dramatically increased.

Well, not all my addons - turns out though my Scriptish has been installed since Firefox 3 (now at 45), it wouldn't reinstall after removal for compatibility problems. Not sure why that wasn't automatically detected, and that may have been the performance issue

[thesmallestcat]

This is an interesting theory! The only scripting thing I have enabled is Greasemonkey, I'll have to experiment more with combinations.