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Issue 1185: When Firebug is enabled, Firefox uses huge amounts of memory and CPU
12 people starred this issue and may be notified of changes. Back to list
Status:  Triaged
Owner:  ----

Blocked on:
issue 5421

issue 2600
issue 2601

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Reported by, Sep 30, 2008
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.

Sep 30, 2008
Project Member #1
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.
Labels: Performance
Oct 1, 2008
Project Member #2
(No comment was entered for this change.)
Labels: needTestcase 1.2
Oct 6, 2008
Project Member #3
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.
Nov 21, 2008
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.
Nov 21, 2008
Project Member #5
Please upgrade to Firebug 1.3,

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+).
Apr 16, 2009
Project Member #6
To make progress this issue needs a test case. 
Labels: Test-case-needed
Aug 28, 2009
Project Member #7
Please try firebug 1.5a22, and let us
know if it makes any improvement.
Nov 25, 2010
Test Case: Firefox 3.6.12, Firebug 1.5.4, Windows 7x64. Few random pages open at . Open new window, try to download a large file (~1.5gb or more). For example . 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.
Nov 25, 2010
Project Member #9
Please test with firebug 1.6b4 at

Honza fixed a problem like this recently. 
Mar 29, 2011
Project Member #10
Marking some of the issues reported about memory use
Labels: memory
Apr 19, 2011
Project Member #11
(No comment was entered for this change.)
Jul 2, 2011
Just changed standard label.
Labels: -needTestcase
Aug 1, 2011
(No comment was entered for this change.)
Blocking: 2600
Aug 8, 2011
(No comment was entered for this change.)
Status: Triaged
Oct 6, 2011
Regarding comment 8:
Could it be, that this issue got mixed up with  issue 3123 ?
Jun 5, 2012
Project Member #16
(No comment was entered for this change.)
Blocking: -2601 -2600 fbug:2601 fbug:2600
Mar 23, 2013
Project Member #17
(No comment was entered for this change.)
Blocking: -fbug:2601 -fbug:2600 fbug:2601 fbug:2600
Mar 23, 2013
Project Member #18
(No comment was entered for this change.)
Mar 23, 2013
Project Member #19
(No comment was entered for this change.)
Labels: -Performance performance cpu
Jul 19, 2013
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).
Jul 20, 2013
Project Member #21 simon.lindholm10
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!
Jul 20, 2013
Thanks simon, that seems to have fixed it! :-)
Jul 20, 2013
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. :-(
Jul 20, 2013
Project Member #24 simon.lindholm10
True, but hopefully  issue 5421  should arrive in a few months and fix that. And it's still usable, just not great.
Nov 22, 2013
Same things appear after update on 21.11.2013. When browsing through the page code and styles, FB really stucks.
Nov 22, 2013
i like how they think this is a "medium priority". lol.
Nov 23, 2013
Project Member #27
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.

Labels: -Priority-Medium
Blockedon: fbug:5421
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