> According to aptitude, I have 443 auto-installed packages that are unused
> that it wants to uninstall.  All but 30+ of these are libs and python
> packages.
> ...
> What about thunderbird.  I never installed a Debian/Devuan version of
> thunderbird, so I can't use the same method as with firefox?  Is there a
> list of required/recommended packages anywhere?

You can run `aptitude show thunderbird` to inspect the package,
it'll list all related ones.

I'm guessing you're also not aware you can run `aptitude` with
no arguments, and then it's a TUI program. It's very useful for
inspecting packages, and will tell you why they're marked for
removal or installation. In situations like yours, I often use it to
interactively inspect dependencies of program's package in the repo
and mark whatever seems important for manual installation.

Looking for info on dependencies wherever you got the program is also
a good idea.