Anyone interested in an unbranded x86_64 build of Thunderbird 3 for Salix64 can find one here.

If you find as I did that links don't open in Firefox, you can set links to open in your desired browser from by going to Edit/Preferences/Advanced and opening the Config Editor. Type network.protocol-handler.warn-external.http in the filter box, right click on the two entries and select Toggle for both. Now when you click on a link in an email you should get a dialog box, from where you can choose what browser will open links.

[edit] current release 3.0.2