There's a small bug. When it first popups to login, close it and then click the little N icon again and it will register that extension login is possible.
Discussion
I'm logged in via extension and it's telling me to login to upload. Ironfox with nos2x-fox extension.
Interesting, if you hard refresh browser does it show a profile to login with in the popup? I may have to test with that setup to see how the flow works