Review for Mailbox Alert by Jay Levitt
Rated 5 out of 5 stars
This is terrific! I have two mailboxes: my personal mailbox, and a mailing-list mailbox. I don't want to get alerted every time a new mailing-list shows up, and with Mailbox Alert, that's easy.
One suggestion: On the Mac, Thunderbird also updates the dock and command-tab icon with the number of new messages. I'd love it if Mailbox Alert could override that, so that I only see new messages in the folders I care about.
To create your own collections, you must have a Mozilla Add-ons account.