The Firefox install through tazpkg removes /usr/lib/libssl3.so and creates a symlink to Firefox's libssl3.so in it's place, however this libssl3.so is incompatible with the current version of Thunderbird.
Restoring the original /usr/lib/libssl3.so over the symlink resolves the issue (and both Firefox and Thunderbird work fine).
Slightly off topic, but how do I get tazbug to work properly? There doesn't seem to be any documentation in the README or man page (or --help) for submitting a new bug. If --bug is ommitted a "no title found" is displayed, but even with --msg I receive the "No description found" error. I've tried everyhing I can think of (--description and other similar flags).