Developer reply by T@ntely
Rated 5 out of 5 stars
Very good with a wide range of options (save/export/import/cloud), but lacking some features such as customization, user-agent settings, and icon selection, similar to ThunderSuite.
I don't know if Thunderbird and his API could use something like Firefox Containers.
Thank you for your review and feedback!
Icon selection is on the roadmap and is currently being tested. It may be released next month.
There are no plans to add user-agent settings, as this would require more permissions for the add-on.
At the moment, there doesn't seem to be an easy way to have something similar to Firefox Containers.
But I agree that it would be a great addition.
I can't promise anything, but I'll add it to the roadmap (at least to check the options).
To create your own collections, you must have a Mozilla Add-ons account.