Rated 5 out of 5 stars
Thanks for this extension! I had exactly the same wish: seeing just the unread folders, but with their place in the hierarchy (and most of all: the account to which they belong). It makes filtering messages into folders lots more useful, and catching up with various mailing lists and communities lots easier (almost a game of making all folders disappear).
To add a feature request: a similar (hierarchical) view for folders with starred messages, and/or messages with a particular tag, would be helpful too, to deal with the (often postponed) "need to follow-up" messages... :-)