It isnt a button, all the 'buttons' in the camera are A's and so as well as disabling them you need to add code in the handlers to 'disable' them, nulling the handler seemed cleaner.

But changing it to a spinner seems like a decent idea and may satisfy https://bugzilla.mozilla.org/show_bug.cgi?id=870726

Will leave that decision for @davidflanagan, happy to make the change, or have this stolen / marked as dup