http://kb.mozillazine.org/Firefox_CPU_usage

1. Run in Safe Mode
2. Remove your old firefox profile and create new one
3. Disable all plugins
4. Disable hardware accelerator

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.

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.

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

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.

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.

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.

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.

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.

Same problem here. Firefox 18 consistently uses all cycles of one cpu core. Downgraded to Firefox 16.0.2 and problem's gone even though I'm using exactly the same add-ons.

It is strongly recommended that old versions of Firefox are not used. Unless you re able to take very strong measures to mitigate the risks such as

• using in a Virtual Machine
• having a well rehearsed bare metal restore procedure

As 46 users have now voted me-too in this thread I wonder if anyone is able to give steps to reproduce, preferably whilst in Firefox's safe-mode.

If there is a real problem, a bug could be filed so that it gets developer attention.

If it does not occur in safe mode, then maybe we may discover in this thread what the cause is and share the solution with one-another.

One contender for the problem will be Firefox's new JavaScript handling. As a troubleshooting step that may be turned of by setting javascript.options.methodjit to false using about:config.

• see http://kb.mozillazine.org/Firefox_crashes#JIT_compiler
  • and http://kb.mozillazine.org/About:config

I too am experiencing high CPU usage since the FireFox 18 upgrade. I'm running Windows 7 SP1 x32 on a P4 machine, so the high CPU usage really bogs things down.

As far as I can tell, the performance hit doesn't depend on how many tabs I have open or which websites I visit. Time is the issue. After a few minutes. CPU usage goes above 90% and stays that way whenever I'm doing something in Forefox. It's really frustrating when I can type faster than the program can echo my keystrokes in a form.

I've tried the standard methods of debugging such problems: starting FireFox in Safe Mode, restarting Windows in Safe Mode with networking, etc. Nothing works. I just can't use FireFox 18 on this PC. I'm not crazy about Chrome, but I've resorted to it because FireFox is just too frustrating to use now (although, to be fair, IE9 is even worse with its constant nagging prompts).

I wonder if this is happening because FireFox is being optimized for performance in Windows 8, and performance in earlier OS versions is being placed on lower priority.

Well, that's just speculation. What's the latest? Has anyone had any success dealing with this problem?

Thanks for your time,

Alan Mintaka

General Note to anyone interested in this thread subject

Please turn on Telemetrymobile Desktop Please turn on Telemetry _{2nd edit}
This was brought out because Mozilla Firefox developer were not being immediately notified of regressions that occurred on the Release channel. Unfortunately on the Release channel the option is off by default so some or the rarer problems still may get missed. Please turn it on it helps developers spot this sort of problem. (It also gives you masses of data you can examine to confirm if Firefox is doing badly)

Alan

Have you tried the steps in my post above to turn of the Java script processing. I am still not sure if this thread is just a self selecting collection of users with differing problems or whether is any real underlying single problem that is yet to be identified.

It would be really good if we could get methods of reproducing this problem that everyone could test, and see, then developers would be able to investigate and fix it.

ESR
I do not like recommending this and must say it is not officially recommended in fact

• it is not supported by this site support.mozilla
• Mozilla states individuals should not use it

But as a temporary measure when the only other Firefox option is to downgrade to an insecure Firefox 17, I personally may try Firefox17 ESR, because at least that remains secure until the problem is resolved and you may return to the Release Channel.

BETA Channel - always has secure downgrade option
Another controversial idea, NOT for now but once this issue is resolved. Use the Beta channel (or be brave and use Aurora also). If an issue emerges in future with a new Beta Release, you see it six weeks earlier and have a relatively easy downgrade option to a secure and working Firefox Release Channel. Having more users on the Beta channel helps everyone as problems are more likely to be found and not get out onto releases of Firefox.

I fully agree with John99 points.

• Please enable performance telemetry
• To further pin this issue down we urgently need to provide a reproducible way to demonstrate it
• It's important not to mix different issues.

For example I tried to reproduce the issue with the mentioned URL http://www.fisiovivax.com. But the fact is: This particular website generates a continuous cpu load on all browsers (tested: FF16, Chrome). So the issue there seems to be with the JavaScript code itself, rather than the executing browser.

Personally, I mostly noticed this issue on internal Confluence Wikis, JIRA tracker and Zimbra Webmailer which are not public accessible and hence a bad problem demonstrator.

Furthermore the situation does not stable arise on just visiting a specific page, but a longer interaction before. I mostly notice the issue on sites, which do some have some sort of in-page interaction like updating parts of the page upon a requests rather than delivering a full new page.

Has anybody more easily, accessible samples and use cases, which are know to have worked fine with FF17 an earlier?

I still do suspect, that my specific might be significantly make it worse compared to a vanilla FireFox installation, due to the large set of plugins I use. But to the large auditorium indicates, that I might be wrong regarding this point.

Looking forward for any helpful hints to better demonstrate this issue.

FIREFOX 19
Note there was for instance a bug affecting bookmarks use with fx18 fixed in fx19. Before embarking on serious troubleshooting it is probably worth waiting for fx19. (It is released but linux users may need to wait a day or so)

TELEMETRY
Someone asked me for further details. Whilst the feature was being tested an add-on was required, now I may view my personal data by keying into the address bar about:telemetry The pooled data collected is also of course publicly available (but you need to register and sign in to the site)

• https://wiki.mozilla.org/Telemetry/FAQ
  • Share data with Mozilla to help improve Firefox
  • How can I help by submitting mobile performance data?
• https://metrics.mozilla.com/

Hello, I have been experiencing the same problem over the past few days. I noticed that with the most recent update (19.0) matters have improved ever so slightly on the whole, but where some pages are using up to 95% CPU I am noticing a significant adverse effect upon other processes (for example, I thought my soundcard/speakers had fried, only to realise that the high CPU usage from FireFox is causing it to pop and crackle - and yes, I have tested this thoroughly to check this isn't the case...)

I have tried disabling Java, which again sees a minimal improvement, but again, not enough to make this any less of an issue.

My main concern is how the consistent high CPU usage inflicted by FireFox seems to limiting my overall use of my laptop. I wonder if anyone has noticed any sound/soundcard related issues?

For the record, I am using Firefox 19.0 on Windows 8 (which has all the latest updates installed). I

Please remember the original suggestion

• that refers to http://kb.mozillazine.org/Firefox_CPU_usage

Also consider looking at the simpler

• Firefox uses too much memory or CPU resources - How to fix

@john99, OK, I've enabled telemetry pre the instructions in the FAQ.

BTW, the link you provide for "Desktop Please turn on telemetry" actually points to the instructions for enabling telemetry on mobile devices (the same link you truck out in the previous sentence).

The link to instructions for desktop clients can be found in the left column of that page. Here's a direct link for anyone who's interested:

Desktop Please turn on telemetry

RE Javascript handling: I'm going to leave that setting alone for the time being in order to provide telemetry for an implementation that has it enabled. I'll turn off the javascript handling after I've used the browser for a few hours, so you can have before/after data for comparison.

Thanks, Alan Mintaka

I went to 90%+ pretty quick, even to reload this page!

I've now changed the javascript preferences shown, per the linked instructions in your message.

Old settings:

javascript.options.methodjit.chrome default boolean true javascript.options.methodjit.content default boolean true javascript.options.methodjit_always default boolean false

New settings:

javascript.options.methodjit.chrome user set boolean false javascript.options.methodjit.content user set boolean false javascript.options.methodjit_always default boolean false

Telemetry is still on. This should generate some before/after results, at any rate.

Thanks, Alan Mintaka

OK, telemetry has been on for over a day now. However when I entered

about:telemetry

in the URL bar, I got this message:

"Problem loading page - The address isn't valid"

Note in my first post that I said I was using FireFox 18. The FAQ doesn't mention that an add-on must be used in order to make the about:telemetry link work in Firefox versions before 19.

I installed the add-on in order to make sure that the telemetry I've been generating with Firefox 18 was actually recorded. After the installation the about:telemetry link started working and I found that telemetry evidently was recorded.

Unfortunately I don't know what to make of the information yet. I did notice at the top of the page two messages followed by a few lines of what look like SQL statements. The messages were:

Slow SQL Statements on Main Thread

Slow SQL Statements on Other Thread

This info was followed by a ton of bar charts, mostly with headers I can't understand.

Should I submit this info somehow, or is it now visible to you guys as well?

Obviously I need to upgrade top FireFox 19. If I do this now, will it erase the telemetry recordings for FireFox 18?

RE the javascript preferences: I didn't notice any change in performance with the Javascript preferences set to FALSE. A few minutes after launching, FireFox started using 90+ % of the CPU continuously, regardless of what I was doing (including just watching the task manager). This wrecked the performance of all other applications on the system, and performance in the browser itself was also lousy.

Thanks for your time,

Alan Mintaka