So recently I was faced with a bit of a snag. A user needed a toolbar installed into his FireFox but FF kept on marking it as incompatible.
As usual, browsers like updating their software without caring about the guys who develop the plugins or extensions. This could become quite irritating if you run a lot of them. The best way would be to wait for the developer to bring out a new version that is compatible with the latest version of the browser in question.
However, if you really want that plugin or extension to work, this is how you do it:
1) Open a new tab and type in “about:config” in the address bar.
2) Click on I’ll be careful, I promise! button at the warning prompt.
3) Right click on the window, and select New -> Boolean.
4) Enter extensions.checkCompatibility.4.0 as the preference name.
5) Set its value to False.
6) Proceed to install plugin/extension in question.
PLEASE NOTE: It’s important to understand that not all extension will work perfectly in new version of Firefox, especially when it’s been tagged as incompatible.