Starting with Firefox 10, add-ons are supposed to be treated as "Compatible by default" during the Firefox upgrade process. For some reason which I haven't yet figured out, this wasn't working right for my add-on, and the add-on was being flagged as incompatible, even though it works fine on Firefox 10.

I have now marked the add-on as compatible up to version 12.* of Firefox, on the add-on website. Try updating Firefox, and let me know if you still get a message about the add-on being incompatible.
Thanks, Darkoshi