Update notification shown after brower update

[Michael K.]

With version 3.1 the handling of new installation vs. updates was changed. This caused a problem that with a browser update the notification is shown that the add-on has been updated. Of course this notification should only been shown if the add-on has actually been updated.

[Michael K.]

Working on the notifications also showed that those had not been localized yet.

[Michael K.]

@alexandre_lapeyre : May I ask you for a french translation of the two new strings? :-)

[alexandre_l]

Of course :-), i'll send you a pull request soon.

[Michael K.]

fixed with version 3.1.1