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Performance Regression: After update to FireFox 18 permanent high CPU load

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Performance Regression: After update to FireFox 18 permanent high CPU load

After the last update FireFox started to continuously eat a whole CPU on my 2-core laptop. My usage pattern (regarding browsed sites and/or activated plugins) has not changed, but I must confess that I'm a heavy user of plugins.

I suspect the problem may arise from a changed performance behaviour of a plugin due to the new JS engine of FF18, but how can I easily trace this problem further down. I.e. is there a way to inspect the collected performance data of firefox (activated)?

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New Contributor

Re: Performance Regression: After update to FireFox 18 permanent high CPU load

The upgrade from FF18 to FF19 seems to have solved the problem for now. Performance is much better, even with many open tabs. CPU usage does peak over 90% from time to time, but doesn't stay there longer than a few seconds.

However, I still have the about:config javascript.options.methodjit preferences set to FALSE. I'm going to leave them that way for the time being, until I'm satisfied that the upgrade has made the performance consistently better than it was with FF18. Once I'm satisfied with that, then I'll reset those preferences to TRUE.

I'll post here again if performance goes back down the dumper, with or without those preferences set to TRUE.

Thanks to all who took the time to read my posts and respond!

Alan Mintaka

38 REPLIES
Legendary Contributor

Re: Performance Regression: After update to FireFox 18 permanent high CPU load

New Contributor

Re: Performance Regression: After update to FireFox 18 permanent high CPU load

Example html page that causes high CPU load: http://www.fisiovivax.com/fisioterapia.html

It has JS in it, so I suppose frucade is right.

New Contributor

Re: Performance Regression: After update to FireFox 18 permanent high CPU load

Thanks jayakumars for your response, though I was already aware of that page and the generic advise is not very helpful in my case.

I'm pretty sure that disabling all plugins would definitely change things and I was more asking how to trace the performance problem down rather than having to go through a long and extensive try&error scheme.

@SirMarius: Yes - it apperas somehow related to specific web pages but not in all cases.

New Contributor

Re: Performance Regression: After update to FireFox 18 permanent high CPU load

I use FF always with many tabs opened, min 100, sometimes up to 300+. After Updating FF17 to FF18 I've recognized a much more higher CPU-usage.


This issue doesn't occur as long as there are just a few tabs opened, or it doesnt' be of any consequence at least. The CPU-load of FF18 gets higher with each opened tab. When you close the tabs, the CPU-usage also gets normal. There is nearly no Flash-content and just few JS working on the websites (thanks to NoScript and ABP).


The System: i5-CPU, 16GB RAM, Win7 x64

FF17.01: CPU-load 1.0% average at 300 tabs

FF18.01: CPU-load 10.0% average at 300 tabs FF18.01: CPU-load 5.0% average at 150 tabs FF18.01: CPU-load 3.3% average at 100 tabs


A fresh install and disabling all addons (even in Safemode) didn't fix the problem. It seems, that FF is permanetly doing something with the tabs to being able to speedup on user-action. It's all good, as long as there are just a few tabs opened, but it's getting worse with each further opened tab.


I've opened a bug-ticket at https://bugzilla.mozilla.org/show_bug.cgi?id=832864

Site Moderator

Re: Performance Regression: After update to FireFox 18 permanent high CPU load

Try to boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that helps.

New Contributor

Re: Performance Regression: After update to FireFox 18 permanent high CPU load

I have to keep my system the next few days on, but I'll try your advice as soon as possible. Anyhow, what is your reasoning behind this hint? Any elder FF versions are working fine, and the system is best maintained.

New Contributor

Re: Performance Regression: After update to FireFox 18 permanent high CPU load

I'd also rather suspect the issue caused by the revamped JavaScript engine rather than any OS issue. @1394: As you bug report was already rejected due to missing details for reproducing it, maybe at least try to assure that you allow FireFox to send performance monitoring data to the developer team (check that it is enabled via preferences > extended (?) > general). I still hope this helps them to spot the issue on their own.

New Contributor

Re: Performance Regression: After update to FireFox 18 permanent high CPU load

Yes I also suspect that the new JavaScript engine has it's glitches regarding CPU usage. We are developing a website complete in JS and experienced a have CPU load on certain pages (though no JS beside a few AJAX calls was actually executed according to Firebug) though we couldn't figure out yet what the cause of the problem is.

Site Moderator

Re: Performance Regression: After update to FireFox 18 permanent high CPU load

CPU load on certain pages (though no JS beside a few AJAX calls was actually executed according to Firebug) though we couldn't figure out yet what the cause of the problem is.

It may be worth while testing without Firebug installed. I guess Firebug use could itself increase the CPU load in some circumstances.