Migrated to simply use PopupNotifications.jsm. Additionally, this
changes the behavior to always have two buttons and a remember
checkbox. When selecting allow with remember, it will behave like
the always allow option previously, but when selecting block with
remember, it will move that page into a quiet mode with respect
to Flash - i.e., no plugin overlays will show anymore, and instead
you will just see the plugin icon in the URL bar, which you can
continue to interact with as before.
MozReview-Commit-ID: EUFlI7nM09t
