Firefox - mysteriously spawning new tabs on it's own

Question for Firefox users out there. Have you noticed your Firefox browser has the mysterious habit of spawning new tabs all on it's own? Just recently I've noticed my Firefox is doing this. The thing is, I can never catch it doing it while it's doing it, so far I've never noticed until after the fact. There is a telltale indicator when it becomes after the fact: CPU resources get pegged and computer begins acting quite erratic due to slowdown. Sometimes the computer is so slow and erratic that it might take 10 - 20 minutes for it to recover enough that I can actually click around some places to see why it might be misbehaving....and then I'll eventually see where one of the Firefox browsers has spawned mucho new tabs...sometimes up tto 5, 6, 7 or more. This many tabs tends to hog resources, so this sort of provides part of an explanation for the erratic behavior. Anyone else experiencing this. Currently I'm using Firefox 2.0014 and for various reasons, do not want to update to Version 3.X at this time.