First of all, I did my homework and found those similar questions, but they seem to cover particular firefox addons. My scenario is different: I don't run a ton of addons, but still periodically CPU usage skyrockets to 100% (I have an old single core CPU). I wonder if it is possible to see which tab is the offending one. Generally I don't run a gazillion of tabs, I try to stick to the 7+/-2 common sense rule, but closing tabs one by one and watching the CPU usage is still not very convenient.

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    +1 Same question. The first time i saw a CPU hog i didnt see the same tag the 2nd time i saw it. Worse is the CPU usage is draining until firefox shuts down so closing a tab wont solve it. Also i think closing and using the save tab feature doesnt help and allows it to eat when you launch the browser again – user3109 Nov 4 '10 at 8:01

Heavy CPU usage when you're idle is usually the sign of a misbehaving website (as opposed to user actions taking a long time, which often points to a misbehaving extension). It could be a plugin, or it could be Javascript.

Identifying troublesome sites can be hard. Visually, look for something that moves — most CPU hoggers are there to animate something (automatically scrolling text, rotating ads, movies, ...). (Animated gifs don't use much CPU.)

If you're lucky, the CPU hogger also makes network accesses. These are a lot easier to pin down to a site. Run tcpdump, wireshark, or whatever your favorite network traffic observer is. Web traffic is TCP and usually to remote port 80. This might point to a site you're visiting, or it might point to a site that embeds into a site you're visiting, typically an ad.

Ads and flash are common culprits, so Flashblock and Adblock can save you CPU time.

Chrome runs one process per tab, so there finding a CPU hogger is trivial. It's also faster than Firefox (but even more of a memory hog if you have many tabs open). You might want to give it a try, though it definitely has fewer bells and whistles, so it's not for everybody.

  • I pretty much block ads/flash, so JavaScript is my biggest suspect. Won't give Chrome a try since it seems to report back to Google what I do. – vtest Sep 11 '10 at 10:51
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    @vtest: the only reporting to Google that Chrome does is tell it which links you've clicked on a Google search page if you did the search by typing words in the URL bar. This can be turned off in the search engine management options. – Gilles Sep 11 '10 at 11:30
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    @Gilles: This "only" thing still fits into my definition of spyware, especially if it's enabled by default. While your answer is valuable, please let's stop arguing about the pros and cons of Chrome :) – vtest Sep 11 '10 at 11:42
  • @vtest Check out Chromium or Iron ( srware.net/en/software_srware_iron.php ) to try out Chrome w/o the reporting, if you still want to test it. – Sathyajith Bhat Sep 11 '10 at 15:00
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    @Boris_yo I think reporting features in any app should be disabled by default. Chrome reporting by default is at least a bad design choice if not bad intention. Chrome reporting by default and coming from Google (yea, those "don't do evil" dudes) is just plain hypocrisy. – vtest May 28 '11 at 0:19

Chrome offers a task manager (Shift-Esc).

If you want the same for Firefox, vote for this bug: Need a way for users to tell where time is being spent when the UI goes unresponsive

  • How can one "vote" for that bug? I went there and could not find any voting functionality. – Luís de Sousa Jul 5 '14 at 18:32
  • @LuísdeSousa: When you are logged in, you can see a "(vote)" link in the field "Importance:" – Aaron Digulla Jul 7 '14 at 14:21

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