I updated to the lastest version, hoping it would fix some of the problems. Oddly I did not know about a later version than what I had running.
But it hardly makes a difference. Only Facebook seems to run better, otherwise it's ... bad as the older versions.
When everything was slowing down again, I checked my task manager. Firefox was gobbling up a whopping 500,000Kb+ of memory with CPU usage consistantly above 5-10% (even when I wasn't actively browsing). Other processes such as Photoshop and iTunes (both also running and active) just a fraction of these resources, maybe 1-2% of CPU.
So I closed down Firefox, the normal way, clicking on the "X" in the upper right-hand corner. I timed how long it took the firefox.exe process to finally close. 9.5 minutes, of which five minutes had it using above 500,000Kb of memory and often CPU usage reached above 50%.

What can Firefox possibly be doing that it needs to remain active so long???? Not updating, considering I updated the day before.
I'm going to try it for a while longer, but in the meantime I'm getting used to Chrome and starting to re-like Explorer. I think Firefox will soon be getting the uninstall... it really has gone downhill like a downhill racer with a rocketpack since it first replaced Explorer as my preferred browser.