Actually Firefox 4.0 is new and it has many changes which make Add-on to not work with it, but after a small tweak you can make it work.
Here is the tweak :-
- Open Firefox 4.0 and type
- It will display a security warning just tick the box and click on I’ll be careful, I promise,
- Now right click and click New –> Boolean,
- Now it will ask for a Preference name, type :-
- Now it will ask for a Value just set its value false,
- That’s it, Restart Firefox and all you Add-On will now work and even you will be able to download and install incompatible add-ons.