Change Firefox preferences from the Developer Toolbar

Martin Brinkmann
Oct 10, 2012
Updated • Oct 10, 2012

If you want to change advanced Firefox preferences you have two core options to do so. You can enter about:config in the address bar, confirm that you will be careful and edit away, or edit the prefs.js file located in your user profile directory manually instead when the browser is not running on the system.

Ken Saunders just informed me that there is a third option which I think is pretty cool. You can change preferences from the Firefox Developer Toolbar instead. This works well if you know the preference name and value that you want to set, and not so well if you do not.

The process itself however is faster and easier than that of the methods mentioned above. Let me explain how you would go about it.

You can open the Firefox Developer Toolbar with the Shift-F2 shortcut. This opens a small toolbar at the bottom of the page. It contains an input console as well as links to various tools that Mozilla integrated into the browser. All we need is the console.

The basic command to change a Firefox preference using the toolbar is the following: pref set name value

firefox developer toolbar preferences

The command pref set browser.tabs.onTop false will move the tabs below the address bar in the browser. It is really easy to use, and if you just want to browse a bit, you can do that by using the auto-complete feature here. Once you have entered pref set here you will see a list of suggested preferences that you can edit. When you start typing in characters, Firefox will automatically match what you type with the preferences, so that you only see matching preference suggestions here. When you find the one you are looking for, select it with a left mouse click or the up and down keys on the keyboard and enter to select. Some preference become active immediately, while others may require you to restart the browser before they do.

If you are a fast typer, of have copied the preference name before, you can speed up the editing of preferences in the browser significantly. Just hit shift-F2, enter pref set, paste in the preference name with Ctrl-V, and enter the value afterwards. You need to press enter to send the command to the browser. The first time you do that, you will a warning message that editing preferences can be dangerous. Just accept the warning, and you won't see the message again.


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  1. Paul(us) said on October 11, 2012 at 1:31 am

    Thanks for this great (handy) tip.

  2. Crodol said on October 10, 2012 at 8:29 pm

    Really cool tip!

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