Because the problem happens only every other day or so, it is not feasible to use the safe-mode method to determine which addon might be causing the problem. The safe-mode method is best suited for problems that deterministically happen within a short period after Firefox launching.

There needs to be a diagnostic approach that can determine where in the code Firefox is spending its cycles. Please, Mozilla developers: can you provide the community with a Firefox Profiler? I imagine three new menu items: (1) Turn on/off profiling; (2) clear profiling statistics; and, (3) show profiling statistics.

I have the same issue but here are some more information:

1. This only happened if I have multiple tabs open and one has to be Google search. 2. If Google is idle (no SERP) then all is fine. 3. As soon as I do a search (live search is on) the CPU usage goes up. Once the SERP is displayed the CPU usage continues to creep up. 4. Things get worst if I open a link from SERP in a new Tab, which sends the CPU rocketing to 100% and will not let go unless I close both the SERP and the new tab. 5. Other tabs do not need to be closed and CPU usage goes back to normal once the 2 new tabs are closed. 6. I run WOT add-on, which is the only thing that can possibly have anything to do with SERP. Disable WOT and all is well again!!! 7. Finally this problem has only manifested itself since 3.6.12 upgrade.

Hope this helps.

Cognisant2 - Thank you for your additional info. I do not run WOT so that is not the key cause of the problem. I am not certain about the google part so I will monitor that. I think I also had this problem before 3.6.12 upgrade.

Just had the problem happen again. had 2 tabs open - my normal email and a news paper - so no Google link. Also disabled as many of the add ons as I could but that made no difference. Restrated FF and all OK

Disappointing to still have no response from FIREFOX about this problem. It has been around for a while and probably affects a lot of users. I guess that if there is no solution soon I will have to move to Chrome or similar.

I see this on OS X and Firefox 4. Performance starts out great. But then over night when I come back to my (many tabs) I see CPU utilization oscillating between say 50% and 90% or so. I use gmail and calendar and lots of other stuff of course and usually have on the order of 10-15 tabs open.

Same problem. CPU goes high and the browser gets non-responsive. I have localized the problem by enabling an disabling add-ons. There seems to be something wrong with the Google toolbar. I have been running the browser without this toolbar for 4 days now and everything seems to be OK. Miss the toolbar though.

Interesting point if Google is the ultimate issue. I have abandoned FF for a month now since this is such an aggravating problem. I too, open multiple tabs and also multiple windows for browsing on XP (HP laptop). Whatever the issue, this is critical for those who see it - the browser is no longer usable. I am now at the mercy of IE-8... and it sure is no fun!