Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Is there a way to install a deprecated addon in Firefox?

I remember doing it in Firefox 3 - can't remember how I did it exactly :(

share|improve this question
up vote 1 down vote accepted

You have to add the extensions.check* booleans to about:config in order for them to work.

enter image description here

In the above, moving from 3.X to 4.0 beta to 4.0 and then to an optimized version I compiled myself based on 4.2a I've gathered the above settings, I bet you need to add extensions.checkCompatibility.4.0.

share|improve this answer
That did it! Thanks a lot - now I can install gleebox, can't live without that thing :) – timkl Apr 9 '11 at 8:40
Thank you, looks awesome! – Tom Wijsman Apr 9 '11 at 11:18

I'm not sure if it'll work with FF4, but apparently with older versions it was a matter of going to about:config, finding extensions.checkCompatibility and setting its value to false.

share|improve this answer
extensions.checkCompatibility doesn't exist in FF4. Thx for the idea, though :) – timkl Apr 8 '11 at 11:49
@timmkl - It was never there by default. You need to create it and set its value: about:config | [RClick] New | Boolean – JRobert Apr 8 '11 at 11:56

I hope you are asking about incompatible add ons. If that's so. Install compatibility reporter firefox add on and install your Firefox add on. Now it will be installed!!!

share|improve this answer

While the currently accepted answer is still accurate, it has become a lot more cumbersome with the ever increasing number of newer versions of Firefox. Granted, Firefox handles compatibility better than it used to, and the need to force enable deprecated add-ons is less common. However, in case someone still needs to do this and finds this question, I'd like to give a more modern, easy-to-use answer.

Install the add-on Disable Add-on Compatibility Checks. Then install your deprecated add-on. Before restarting Firefox, be sure that no add-ons you do not wish to use are turned on by checking the Addons panel. After restarting, see if the add-on works. If not, disable it again.

It is possible that Firefox will break in a way that you cannot get to the Addons panel and shut off the add-on. If so, close Firefox by using Alt-F4, wait for it to close completely, and then start it again in Safe mode by holding down shift while you click to open Firefox. Disable the addon in the Addons panel and then restart Firefox.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.