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How to Make Incompatible Add-ons Work in Firefox 4

Firefox 4 has been released by Mozilla with lots of new features like tabs on top. But one thing you might have noticed the moment you started using Firefox 4 is that add-ons from the previous versions are all incompatible. You might have installed lots of add-ons on your previous version and these will not work on Firefox 4.0 beta version. But you can easily bypass this check and make all the add-ons compatible with Firefox 4.


If you open the add-ons page in your Firefox 4 (about:addons), you can see the incompatible add-ons.

Incompatible Add-ons

Open up the about:config page (type it in the URL bar and enter) and then right-click anywhere in the about:config page and choose New –> Boolean.

New boolean

Now in the pop up box enter the following values;

If you are using ;

  • 4.0 Beta- extensions.checkCompatibility.4.0b
  • 4.0 Release- extensions.checkCompatibility.4.0

Boolean Value

Set this value to false.

False value

Now you can make all your previously enabled add-ons to work with Firefox 4. All you need is to restart your browser. With this trick you can also install new add-ons which are still incompatible with latest version of Firefox.

Thanks to HowtoGeek for this tip.

About Nirmal

Nirmal is a Technology Blogger and a Microsoft MVP in Windows. He can be contacted at nirmal@nirmaltv.com. You can find Nirmal on , and .


  1. when is the stable release of firefox 4

  2. I didnt work for me, it still says its incompatible : (

  3. Hello Nirmal,
    “extensions.checkCompatibility” hack did not work for me in firefox 5.0. I wanted to install aardvark in FF5 which is incompatible. I edited the addon file to make it work with firefox 5.0 and wrote a tutorial for needy users. May be it is useful for your readers too so posting a link here


    Hope it helps all who need it.

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