I downloaded and installed Firebird and Thunderbird today.
Excellent software. Lightweight, useful and on-target as far as utility expectations were required.
I'm most interested in Thunderbird because of the generally dismal state of mail clients. I think I may have stumbled on a keeper. Not only does the filtering do what I want it to do, but its easy to add new filters to the rule-set. Further, the filter file is stored as plain-text and gives me the option of replicating it to all of the boxes that I use. The only thing missing is the capability to specify a remote URI where Thunderbird could just sync the ruleset from.
Firebird is great - it hearkens back to the good old days when a browser as a browser and IE still looked like Mosaic.
All in all, the Mozilla project is moving things in the right direction.