What steps will reproduce the problem? 1. Enable Firebug 1.2.1 2. Start Firefox - resume session with multiple tabs 3. Tabs take up to 10x longer to load than when loading exact same session with Firebug disabled; once session is loaded, Firefox uses 3-4x as much memory and 10x as much CPU as when exact same session is loaded with Firebug disabled. This is with Console Logging, Javascript Debugger, and Network Monitoring disabled. Same result when Firebug is suspended (by right-clicking icon in status bar).

What is the expected output? What do you see instead? Expect Firefox to operate roughly the same when Firebug is enabled but not being used (or enabled but suspended); certainly not to become all but unusable because of vast drain on system resources.

What version of the product are you using? On what operating system? Firebug 1.2.1, Firefox 3.0.1, Windows XP SP3, on a system with 4G (3.25) RAM, 2.66GHz quad-core chip

Please provide any additional information below. I understand from researching that Firebug's creator believes that the extension "shouldn't" have this effect on Firefox's memory usage; all I can say is that after extensive experimentation, it definitely is. Working with multiple tabs/windows has become impossible for me (I've been using FF and FB for years; this was not the case for me with older versions of FB under FF 2.0 - of course, I kept FB mostly disabled then). The only solution for me is to disable it; when I need to work on it, I shut down FF then reopen a single window with a single tab and enable it. Very frustrating. Something is wrong somewhere.

Ok, but what do you propose to do about it? I open firefox with Firebug twenty times a day and I don't see any of the effects you describe. Moreover with the panels disabled and firebug suspended the scope of things that could cause 3x memory are very small.

But lets back up here. Lets talk about a specific set of URLs. Pick one with the most impact on memory (or CPU). Lets compare numbers. You'll have to start with a new Firefox profile and only Firebug 1.2.1 installed. Firebug enabled vs Firebug disabled: what is the real delta? If you have one I'll try it.

See also Issue 867 I've worked hard on performance issues. I've investigated many reports of extraordinary performance problems and fixed any issues I can. So far as I have found the uses of memory and CPU are just what one expects. Based on this experience I am skeptical until someone comes up with a specific test case that shows a problem.

I have the same problem with Firefox + Firebug on Ubuntu Linux 8.10 on amd64 arch. I'm using Fx 3.0.4 and Firebug 1.1.0b12. When Firebug is enabled Fx uses 200 to 500 MB of memory for 7-10 simultaneously opened tabs (no special URLs - all different stuff is involved). Without Firebug Fx uses 130-150 MB of memory. I also fully confirm that Fx sometimes hangs especially with slow Internet connection, when process of loading pages is slow.

Please upgrade to Firebug 1.3, http://getfirebug.com/releases.

The memory that Firebug uses is mostly records of net traffic. If you don't want these to be recorded, disable the net panel. (requires Firebug 1.2+).

To make progress this issue needs a test case.

Please try firebug 1.5a22, http://getfirebug.com/releases/firebug/1.5X and let us know if it makes any improvement.

Test Case: Firefox 3.6.12, Firebug 1.5.4, Windows 7x64. Few random pages open at http://download.oracle.com/javase/tutorial/uiswing/index.html . Open new window, try to download a large file (~1.5gb or more). For example http://centos.mirror.netriplex.com/5.5/isos/x86_64/CentOS-5.5-x86_64-bin-DVD-1of2.iso . Watch firefox memory use using taskmanager, it will continue to increase approximately the same amount as has been downloaded until Firefox hits about 1.6gb in use and it stops responding. Pausing the download will pause the increase. Disabling firebug stops the memory increse/hang and allows download to complete. Test has been repeatable many times, for many different large downloads.

Please test with firebug 1.6b4 at http://getfirebug.com/firebug/releases/1.6x

Honza fixed a problem like this recently.

Marking some of the issues reported about memory use

Just changed standard label.

Regarding comment 8: Could it be, that this issue got mixed up with issue 3123?

I'm having this problem with Firebug 1.11.4. Anytime I open Firebug it takes a really long time. Sometimes I see the beachball on OS X. It has to do with the Console. If the console is disabled, this doesn't happen. I'm using Firefox v23.0 (beta channel).

That seems more like a description of issue 6086. Issue 4978 should fix it unless you have the Script panel enabled, so try the 1.12 beta!

Thanks simon, that seems to have fixed it! :-)

Yeah, you're right about the script panel. The console loads fast now, but enabling the Script panel causes the CPU to spin out. :-\

This means that Firebug is still not very useful for its designed purpose. :-(

True, but hopefully issue 5421 should arrive in a few months and fix that. And it's still usable, just not great.

Same things appear after update on 21.11.2013. When browsing through the page code and styles, FB really stucks.

i like how they think this is a "medium priority". lol.

Formerly when a new issue was created, it was automatically marked with "Priority-Medium". As Simon already wrote in comment 24 issue 5421 will improve the situation, which has our top priority.

Sebastian