Firefox offers lots and lots of add-ons developed by enthusiasts all over the world and that is why, Firefox keeps a check whether the add-on you are installing is compatible with the installed version of Firefox or not. This does not entirely mean that the add-on will not work altogether. But some of its functionalities may get compromised and that is why Firefox won’t let you install the add-on in the first place. However, if you still want to try an incompatible add-on on your installed version of Firefox, you need to follow the steps below.

1) Open Firefox, write ‘about:config’ in the address-bar and press Enter.

2) Bypass the security warning by clicking ‘I’ll be careful, I promise’ (duh!). Now you will see a big list of configuration options. Right-click any where and select ‘New’ > ‘Boolean’.

3) In the window that appears, enter the preference name as ‘extensions.checkCompatibility’ and click OK.

4) Double click the entry to make its value ‘false’.

That’s it. You’ll now be able to install incompatible add-ons in Firefox.

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Be careful, you are now vulnerable to every kind of mess up. You may find yourself fixing your browser for the whole day if you install a really bad incompatible add-on. 

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