I just fired up Firefox to do a bit of writing over in the project wiki, and as sometimes happens, I was presented with an extension update notification screen. The UI is mostly a farce of user control in that there's not nearly enough information to judge whether or not going to the next version of Me.dium is a good idea or not. I blithely click "OK" to let it do it's installation dance in the hopes that it'll get out of the way. I've got stuff to do. It dutifully proceeds.
A couple of seconds later, it's done, and instead of getting an unobtrusive notification of success while the browser starts to load whatever it is that I actually care about, the update window simply shows a nearly identical UI, but the button that had previously allowed me to proceed with the upgrade now reads "Continue". Do I have a choice at this point? What would closing the browser at this point ever buy me over hitting "Continue"?
Given the massive number of Firefox users and their use of extensions, it boggles the mind to think how much time is wasted by this one button alone. Unless there is an affordance for recoverability (roll back the upgrade) or discoverability (what just happened?), this button needs to die.