Firebug can make Gmail slow

Martin Brinkmann
Nov 7, 2007
Updated • Mar 19, 2014
Email, Firefox, Gmail

If you use Firebug and visit Google's email service Gmail, you may receive the message "Firebug is known to make Google Mail slow unless it is configured correctly".

The message was new to me and I decided to investigate the issue. Firebug is a popular web development extension for the Firefox web browser that you can use for all kinds of development related things such as inspecting the HTML or CSS code, debugging JavaScript, analyzing network usage, or inspecting individual elements of a web page.

Google suggests to disable Firebug for the Google domain completely which should not be a huge problem, unless you use it on it, for instance to analyze the code on the site, check up on Gmail's performance, or alter code on it whenever you visit it.

Update: Please note that the message is no longer displayed when you visit Google with Firebug installed in the Firefox browser. The main reason for this is that Firebug does not run automatically anymore on all sites you visit. While you can enable it to run on all sites you visit, that is a choice that you have to make actively. Update End

To do this you simply right-click the green Firebug icon in the status bar and select "Disable Firebug for". Another option offered by Google would be to disable certain features of Firebug while visiting Gmail. Those are the Show XMLHttpRequests and Disable Network Monitoring options.

I was not able to verify any slowdowns with Firebug and was not able to verify any speed ups after disabling Firebug when visiting Gmail. I suppose some users can experience them and this is why I thought it would be nice to post this information.

To disable the options in Firebug you do the following:

1.Click the green or red icon in the bottom right corner of the browser window to open Firebug.
2.Click the Console tab.
3.Select Options.
4.Uncheck Show XMLHttpRequests.
5.Click the Net tab.
6.Select Options.
7.Check Disable Network Monitoring.

Update 2: Again, this is no longer necessary as Firebug will not run on Gmail by default. You need to left-click on the icon of the extension to enable it on the current site. That's probably the core reason why there is no option anymore to disable domains in the extension.

The two features do not need to be disabled as well, as they do not run when you visit Gmail using Firefox and Firebug unless you enable them actively first.


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  1. John Barker said on June 26, 2008 at 4:05 am

    I’m using FF3 and firebug 1.2.0b3 and often see slowness (sometimes even crashing firefox) when firebug is enabled.

    I haven’t tried the method listed above, but I find it easier just to keep firebug disabled when I’m not actively using it.

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