I use Tutanota as my main email provider. The problem is that every time I open my mail, I get a pop-up with a message from Firefox suggesting that Tutanota manages my mailto links. AND I DON'T WANT IT, you can click as many times as you like on the little cross, this pop-up will continue to appear, forever.
I've even written a tutorial on how to disable this from the `about:config`!
On the same pop-up, a "Don't ask again" option should be displayed to automatically deactivate the parameter in the `about:config`.