Would be great if Microsoft didn't break it (Outlooks loads indefinitely).

INSTALL IT!! Open your Protonmail in Firefox, click the banner in the browser to make it your default mailto:. Then you can also select certain emails to open work emails in Outlook, and you can still open Gmail from mailto: links as well. So, you can use ALL THREE(3) !!! Love it!

Good plugin that allows you to chose your desired email application, 5 stars.

The plugin is in good design and make my life convenience :)

Awesome plugin which enriches the user experience of clicking on the email links and tel numbers. Well done!