Last week I got a new MacBook Pro to replace my (two year) old one. Among the problems with the old machine was a perennial lack of space on the hard drive. I kept having to compress, archive, and throw away files to keep myself (barely) in the black.
The new machine's drive is twice as big, and that means plenty of space to build updated packages of Thunderbird 2 with my tabs patch based on the just-released Thunderbird 188.8.131.52. The packages are available for Mac OS X, Linux, and Windows.
If you are the adventurous type, however, check out the Thunderbird team's 3.0 alpha releases, which have tabs built-in by default. And note the discussion on an experimental message view that aims to come up with an even better approach to opening multiple messages.
Incidentally, I'm standing on the shoulders of giants here. The only reason I can build these at all is because Mozilla's build/release team puts hard work into maintaining a build system and toolchain that makes it relatively easy to compile this several-year-old codebase even on new hardware running recent versions of all three operating systems. Kudos and many thanks to them.