Review for Gmail Manager by Wolby
Rated 4 out of 5 stars
I like this add-on a lot-- use it all the time. I have to say, however, that it is rarely working 100% correctly. If it's not displaying 0 unread messages (which is never true for me), it's mixing up my two accounts (right now they both have the same message count and subject listing) or something else odd.
In the vein of suggestions, I would love a feature where only the titles of unread e-mails in the Inbox are shown on mouseover.
To create your own collections, you must have a Mozilla Add-ons account.