So something is still wierd about extensions and the mail.google.com
domain. The SimpilyGmail extension works (sometimes) so extensions can work (but every so often it stops). The Raindrop.io extension can't seem to get the "url" of the current tab to bookmark (though unlike before, you can actually activate the extension).
Raindrop.io extension on a gmail page:
(No title, no URL, completely empty).
Here's the extension on a youtube url (so both google properties)
At this point (with SimpilyGmail working most of the time), it's no longer a blocker, just some odd behavior.