Rated 4 out of 5 stars

Disclaimer: I'm a sucker for Thunderbird extensions. I wish there were more of them :) This add-on is very well-done, meaning that it has a professional, just-what's-needed UI that adds just about every piece of information about an e-mail as a potential column to be displayed and sorted on. I've already used it in a number of ways. I put 'account' as one of the columns for a smart folder that transcends a single account, for example.

The only reason I gave this 4 stars instead of 5 is that I believe 95% of Mozilla add-ons should have allow the user to select preferences. In this case, it could be as simple as choosing which extra folder columns to list and which to exclude. Granted -- this isn't critical but I imagine that most users prefer to have some control over add-ons, even if they aren't entirely necessary. Overall, a nice addition to Thunderbird and I'm going to check out what else these author's have to offer. Thanks, guys!

This review is for a previous version of the add-on (1.1). 

@linefeed: You can already select which columns you want - just click on the little box at the right-hand end of the folder column names and you'll be able to choose the columns you want.