Review for mailmindr by Berti
Rated 3 out of 5 stars
The add-on is *very* useful and allows me to easily set up reminders to follow-up on some email.
Unfortunately, when the add-on is enabled, some of my mailboxes can no longer display the emails in their folder. When I select a folder, the email list is shown briefly (for 1-3 seconds), then the list goes blank. Saved searches work as workaround, yet I have no idea how to debug this.
To create your own collections, you must have a Mozilla Add-ons account.