Make Incompatible Extensions (Add-Ons) Work With Firefox 4 Beta

Mozilla Fireox Add-OnsFirefox is a great browser, but one of the biggest annoyances with Mozilla is the Add-On support for beta versions. Whenever you try to download an Add-On made for an older version of Firefox, your newer version will receive the well-known error message: “…could not be installed because it is not compatible with this Firefox.” Well, now we’ve got an easy way to fix this by using a simple trick that allows us to disable the Add-On Compatibility checker.

How To Disable The Firefox Add-On Version Checker



Step 1 – Start Firefox

First of all, you will need to call your trusty companion – Firefox. For XP, simply go to Start > All Programs > Mozilla Firefox 3.6 Beta 4 > Mozilla Firefox. Of course, if you are running Vista or Windows 7 you can always start it up more quickly by opening the start menu and typing in Mozilla then Pressing Return.

Opening Firefox



Step 2 – Go To The Mozilla Configuration Page

Now open the Mozilla Config page by typing about:config into the address bar. A warning will appear notifying you that you are now in the most serious parts of Mozilla. Go ahead and click “I’ll be careful, I promise” to move along.

Opening The Firefox Configuration Page



Step 3 – Create The Compatibility Check Boolean

An extensive list of items will appear. Right-Click anywhere in this list and select New > Boolean.

Creating the Firefox Boolean


They ask you for a Boolean value. Type in:


Enterning The Boolean Value

Press OK. “4.0b” stands for version 4.0 Beta. Whenever you need to use another version, simply change the numbers to your current Firefox version. Make sure to add a b if it’s a beta!


Next, make sure you mark false in the next dialog so that you disable the compatibility checker. Click OK, and – finished here!

boolean value false



Step 4 – Restart Firefox

Close Firefox and Open it again. Try out any of the older extensions now. They should begin to install, and you will be able to enjoy your favorite Add-Ons once again.



Even with groovy new Add-Ons developed more and more very day, there are still some old Add-Ons that you cannot replace. That’s why we think this trick will be at the top of the Mozilla tricks list for every regular Firefox user.

If you’re interested in Web Browsers, make sure to “stay tuned” for our upcoming review of the “Google Chrome Power List” – all the Chrome extensions you’ll need to use Chrome like a PRO.



  1. Ben

    September 1, 2010 at 6:00 pm

    I’m running FF4 Beta 4 and every time Firefox is restarted (or closed and opened again), the extensions.checkCompatibility.4.0b value in about :config is set back to true, instead of false.

    Anyone else running into this? It is annoying as hell!!!

  2. lionjimi

    February 25, 2011 at 8:55 am

    Firefox is a great browser, but one of the the biggest annoyances with Mozilla is the Add-On support for beta versions. Whenever you try to download an Add-On made for an older version of Firefox

  3. India Phone Cards

    August 23, 2011 at 12:50 am

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  4. Olyfah

    February 10, 2012 at 11:07 pm

    that must be a joke, just ilsatnled it from market. it’s slowest, buggiest and laggest app on android ever.

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