If you have ArcadeOX installed in Firefox 3 and try to upgrade to Firefox 4 you will be told that it is incompatible. You can disregard the incompatibility message, it is incorrect.
If you do see that message while upgrading then you will have to perform the following steps.
In Firefox
- Click Tools.
- Select Addons
- Select Extensions
- Select ArcadeOX
- Select Remove
- Restart Firefox
- Play a game
- Click Free Download
- Click Allow
- Click Install Now
- Restart Firefox
- Play a game.
Make sure that it does not say ArcadeOX is disabled in step 4.