Eddy, i can certainly try disabling the FF add-ons, but you should know that i am currently running AVAST with the "browser protection" disabled. Is it still worth the test?
Also, i just booted up my PC and brought up ThunderBird. The only application running was TB and it had already downloaded any E-mail waiting to be processed, yet AvastSVC.exe was using 99% of the CPU (before i even tried bringing up FF). Now, from past experience, i know that if i try to bring up FF when AVAST has the lions share of the PC, it will take forever and in fact took 5.5 mins to come up. I do not think that FF is the problem here!