Rated 3 out of 5 stars

Not bad BUT if we receive any mail, we are not notified.
Protonmail ask to allow desktop notification but of course we can't.

Thanks for the feedback, this is a simple extension that opens Proton mail in a new tab as mentioned in details and notifications is related to Thunderbird browser you can find more about how to activate it here;
https://github.com/tdmrhn/Thunderbird-Quick-Access-Buttons/issues/9