Have you been excited about a new nightly build of Firefox, gotten it set up on your computer, and then found out that you can not install your favourite extensions? Say goodbye to that frustration! With a little tweak to the about:config settings, you can get those extensions installed and working.

Trouble Adding Your Favourite Extensions

After you have just installed your new nightly build of Firefox, a quick check of your version should look like this.

But when you go to install your favourite extensions, you see a message that looks like this (Delicious Bookmarks extension used here).


That is definitely frustrating, especially if it is one of the extensions that you use on a daily basis. Now what do you do? Fix the problem with a little bit of tweaking magic.

Tweaking the about:config Settings

You will need to type “about:config” (without the quote marks) into the address bar and hit “Enter”.

The first thing you will see in your browser window will be this message warning against making changes to the about:config settings. Click on “I’ll be careful, I promise!”.

Once you have clicked through, your browser window will look like this.

It may seem a bit overwhelming at first look, but the change that needs to be made is simple to do. Now that you have your about:config window open, right-click in the browser window area and select “New –> Boolean”.

As soon as you select “Boolean”, you will see the following window asking you to “Enter the preference name”, enter/paste “extensions.checkCompatibility” (without the quote marks) and click “OK”.

Once you have clicked “OK”, you will see this window. The default should already be set to “false”, but if not select “false” at this time. Click “OK” again and your new about:config setting will be all set up.

As soon as you have clicked “OK”, you will see the new about:config value highlighted in your browser window like this.


Now you are ready to install your favourite extensions. Once you have finished installing them, opening up the addons window will reveal the following message listed for each of your newly added extensions. While it will say that your extensions are not compatible, you should have no problems with your extensions functioning as normal. This should get you up and running to have lots of fun with your new nightly build of Firefox!

Note: Only on rare occasions will an extension not function correctly or exhibit odd behaviour.

Get the latest Mozilla Firefox TraceMonkey Nightly Builds

Akemi Iwaya
Akemi Iwaya has been part of the How-To Geek/LifeSavvy Media team since 2009. She has previously written under the pen name "Asian Angel" and was a Lifehacker intern before joining How-To Geek/LifeSavvy Media. She has been quoted as an authoritative source by ZDNet Worldwide.
Read Full Bio »