The story begins with the release of Firebug. I love it as a tool, but Firebug + Firefox are the killer combination.

Let me start by introducing two system reports: 1) CPU 2) RAM usage.

cpu ram usage

  1. I've been living with 8GB RAM for few years. During working hours (using Firefox for development) my free RAM would go as low as 100MB or worse. Most of the rest being "inactive" (approx. 3GB).
  2. I bought 16GB RAM DD3 expecting to forget any lag while typing into textarea. This didn't work. FF10 uses mostly 2 GB RAM, then takes loads of inactive memory and continues to lag. Take more but stop lagging!

My question is:

  • Is it really Firefox to blame?
  • How do I force Firefox (and all other apps) as much RAM as they need but just stop lagging.
  • Why Google Chrome (and most other modern browsers) can do exactly the same as FF+FB using only ±200MB RAM?

Thank you

  • 2
    Firebug does have memory and peformance issues, that's a "known problem". I recommend disabling it when you don't need it. – Wladimir Palant Mar 1 '12 at 18:18
  • The problem is I need it literally every time I use Firefox. Otherwise I just use Google Chrome. – Gajus Mar 1 '12 at 18:30
  • Chrome bloats to 1GB with addons after a workday, too. – dnbrv Mar 1 '12 at 18:39
  • I'm afraid I have to agree with "This is just because Firebug is poorly written" – Shinrai Mar 1 '12 at 18:48
  • @dnbrv After a work day, not after 10 minutes. – Gajus Mar 2 '12 at 14:33

Firefox leaking RAM like that is almost always a sign of a buggy plugin or addon, especially with all the efforts from the MemShrink initiative over the past several months and releases.

The fastest (but least fun) way of debugging is to create a new profile. If the behavior persists, disable all 3rd party plugins.

If it still persists then there may be a Firefox bug. Otherwise it's a matter of slowly re-enabling plugins and re-installing addons until you find the culprit.

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  • 1
    afrazier, There is literally nothing else on Firefox except Firebug and Adobe Flash. – Gajus Mar 1 '12 at 18:32
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    Have you tried creating a new profile yet? It's literally step #1 in Firefox troubleshooting. It doesn't matter how much or how little you have. – afrazier Mar 1 '12 at 18:42

This doesn't look like a memory problem, rather you're simply running out of sequential processing power. The Activity Monitor output shows Firefox with 68% CPU usage, but the system as a whole has 89% idle CPU time. That tells me that whatever Firefox is doing can't be easily parallelized, otherwise the code would be running in some of those 27 threads Firefox has, and using a lot more of your idle CPU cores. This in turn would push Firefox CPU usage way over 100%, which is what I see with other CPU-hungry multi-threaded processes.

So, in summary, Firefox with Firebug enabled is one of those serial processes that, as predicted by Amdahl's Law, isn't helped much by having multiple CPUs.

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  • The problem is multi-core system? What is the solution then? – Gajus Mar 1 '12 at 18:33
  • The problem isn't in the multi-core system. The problem is in the software. – dnbrv Mar 1 '12 at 18:39
  • 2
    And that software is some software is hard (or impossible) to effectively multi-thread. – afrazier Mar 1 '12 at 18:42
  • And that firefox's decision to run everything in one process.. really sucks, which is why actually google chrome is so snappy - it just launches tons of processes (one for each site, roughly). – qdot Mar 1 '12 at 21:44

I regularly use Firefox with Firebug and some other 30+ extensions enabled, 50/100+ tabs open and have no such issues (3GB RAM, WinXP).

From my Firefox experience, what can I advise:

  • if you have your profile for a very long time (say, same profile since Firefox 3.5), you should probably clean it up a bit. New versions of Firefox sometimes change various stuff, therefore some files are no longer necessary etc. Creating a new profile is a good point to check if there's any difference, and to compare the contents of the folders and so on,
  • the above is especially true if you had uninstalled some extensions,
  • use Vacuum Places Improved to clean up your bookmarks, CTRL-SHIFT-DEL to clean the cookies, cache, history,
  • memory consumption grows rapidly (and memory is not deallocated, and browser slows down heavily) when you visit pages with huge images (several Mpx+).

As I mentioned before, I have 30-40 extensions enabled and everything's quite fine. I used to have some problematic extensions, but I spent some time to track them down and uninstalled.

Generally, Firefox doesn't go above 1GB of RAM, unless I open pages with huge images / lots of Flash content.

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