The key to the fix is to prevent Firefox from checking its version number before it tries to load extensions. To do this, you will need to set a new preference value. Point your browser at the URL "about:config", then right-click on the preferences list to bring up the contextual menu. You should see an option that says "New." Select that, and choose "Boolean." When it asks you for the preference name, type "extensions.checkCompatibility" (without the quotes). You have to enter the name exactly. For the value, choose "false."
Don't forget to restart the browser after applying the fix.