With Firefox 3.6, Mozilla has changed the way users can override the default add-ons compatibility check.
WARNING: Bypassing the built-in add-ons compatibility check thus forcing Firefox to allow the installation of incompatible add-ons can cause Firefox to become unstable and/or run erratically. In some instances, could cause Firefox not start at all. In the event forcing an add-on to install has lead to Firefox perpetually crashing upon startup the browser can be run in Safe Mode, which will allow for the removal of the problematic add-on.
Bypassing the compatibility check can be done via an about:config entry. However, this will need to be done for each version (3.6, 3.7, 4.0, etc.) as there is no longer a universal setting.
- In a new tab type about:config in the address bar and press enter
- Right-click in an empty area below the filter bar and select New -> Boolean
- In the New Boolean Value dialog box type: extensions.checkCompatibility.3.6 and click OK
- Select FALSE and click OK
- Does not (currently) work with Firefox 3.7/4.0 developmental builds
- The value entered in step #3 will need to be changed with each newer version of Firefox. Example: Testing the developmental Firefox 3.7 Alpha builds the value entered would be: extensions.checkCompatibility.3.7a and this would need to be changed to extensions.checkCompatibility.3.7b when moving to the Beta builds and changed again to extensions.checkCompatibility.3.7 with the release of Firefox 3.7
- For testers it is recommend to use the Nightly Tester Tools extension instead of performing this tweak.
Source: CyberNet News