Created attachment 8642111 [details] userChromeJS-2.0.xpi The error reason isn't known, it's likely not valid, but an immediate retry gets duplicate uuid. The xpi is attached.
Also, despite the error, I got the following email: Your add-on, userChromeJS 2.0, has passed our automatic tests and is now signed and ready for you to download at https://addons.mozilla.org/en-US/developers/addon/userchromejs/versions. ..but there's nothing there.
It looks like you didn't finish the upload process (due to the error you ran into), and it needed to be finished before your listing became visible. It should be fixed now. Try visiting the URL you got in your review email and let me know if you still have any problems.
The signed version is there and works without warnings fine on Fx trunk, thank you.