How to force Firefox extensions to be “compatible”


FirefoxextensionscompatFollowing our early morning post regarding Firefox 3: you may find that upgrading to the new version will make some of your extensions incompatible as James already found out. This is common with any Firefox upgrade and you can bet that developers will work to make their extensions work with the new version as quickly as they can. Until then, you can tweak Firefox 3 to at least allow your older extensions to install if it first doesn’t allow them.

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FirefoxbecarefulFirst you need to type “about:config” in the URL bar in Firefox 3. Note: no quotes when typing this. You’ll be warned that you’re mucking about with the settings. Just click the “I’ll be careful, I promise!” button and you’ll see tons of application preferences.The one you want actually isn’t there, so don’t bother looking for it. Instead, right click to create a New, Boolean preference. Type “extensions.checkCompatibility” (again, no quotes) as your preference and then choose the value of False for it. Restart Firefox and you should be able to install any Firefox extension.This doesn’t mean that your older extension will work perfectly; after all, it was designed for Firefox 2 or earlier. However, you can at least install and try it. In fact, my gut tells me that this preference is to aid extension developers, which is why it’s not included by default.Remember that you could hose up your Firefox settings and behavior with these types of tweaks, so if you’re not willing to take and accept that risk, stay away from “about:config”.


Mark G

This was simple and worked perfectly. Question: any downside to making this change? I’m guessing it won’t automatically stop old programs from being installed, so I’ll just have to “manually” decide whether to run the risk of installing an old program, but otherwise, no problem leaving the change; is that right?

And thanks!


I have several extensions that are incompatible with Firefox 3.0, but the uninstall button is disabled so I can’t remove them. Is there a trick for re-enabling the uninstall button?


This is nonsense, it is a good trick. It’s a really bad habit, to try to protect the user from himself. If he wants to do something risky, tell him it’s risky and let him choose but don’t treat him as if he were a kid.

Brian King

This is not advisable, because it has the potential to make Firefox really unstable. Then Firefox gets a bad rap for something that is essentially not their fault. You could argue that the back door should not be there, but that is another story.


A really good trick! One of the reasons why I have not switched to FF3 is because I have some extensions that I can´t live without.

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