I click an email in Firefox, then go back to the inbox, try closing the tab, says something about Gmail doing something, click OK, and the email is still not marked as read, as the notifications is still on my phone.

And it’s not marked as read in Firefox either, just checked.

Looks like the shittiest email you can get. Guess I should forward it all to my iCloud email, and get rid of the Gmail app.

It was probably designed intentionally to be like that, as it probably works fine in Chrome.