This is a very easy to use, privacy enhancing feature. Once you've setup the whitelist, you don't even notice it doing its thing in the background anymore.
Notifications available for nerds like me who like to know that stuff. A great addon, thank you.

Finally I can open Gmail tab and be sure not to stumble into any mailbox left open by my wife or son previously.

Delayed autodelete is also precious, just set it to a quite long time (i.e. 5 or 10 minutes) and you can still reopen that mailbox tab you have mistakenly closed, without having to retype your credentials.

Thanks so much for this addon!

PS. A BlackList feature would also be appreciated. I often need to delete cookies only for particular sites (i.e. webmail sites, social networks, etc.).

works
works with the Firefox Container
simple GUI
can recommend it to everyone

GUI of this app has a potential to improve. I mean, current state can't be considered as satisfactory. I even gave 1 star to this extension at first :) It easy to mess with it's configuration and be forced to login again to whitelisted sites.
But eventually i stayed with this extension, cause it's the only one i found to be functional on mobile devices. So it's OK, compared to others.

Works but what I would like some option to automatically add all cookies to the whitelist since i don't want to go to all sites and whitelist them.

Marvelous!

Please add a blacklist feature where it just deletes chosen sites