One annoying feature, so far: an RSS feed (e.g. from Business Week) comes up well in Thunderbird, i.e. it looks like it would in Firefox. However, when I click a link, it brings up a new tab in Firefox — not in Thunderbird. This is actually more-or-less what used to happen when I had the e-mail subscriptions sent to my Lotus Notes e-mail client, and clicking the link there would bring up a page in Firefox. Now that I can use Firefox to view RSS feeds more directly, reading has been a lot smoother.
A web search has turned up Myk Melez working on tabbed message browsing in Thunderbird. This would seem to be what I want to do.
Unfortunately, this isn’t part of the main Thunderbird development plan, and Myk is working on this as a side project. His available download isn’t an installable, but instead a zip file. I think that I could just copy the unzipped files on top of my current Thunderbird installation, but it doesn’t feel right, at the moment. There was a note that tabs would be part of Thunderbird 2.0, but it would be nice if this could be packaged as a Thunderbird extension until then. (I don’t understand the architecture well enough to know if that’s possible).
Myk only posted this starting in December 2005, so I think that I’ll subscribe to his blog, and watch out for progress.