OK! I fixed my Thunderbird Mail application!
Here’s the problem: On the USB stick, applications are installed to the /data directory. So, when Thunderbird is set up, it installs everything to /data/home/username/.thunderbird. When Nomad is installed from the USB stick to the computer’s SSD or HDD, there is no /data directory. Root is installed to /. All the thunderbird configuration files are there at /home/username/.thunderbird, but when Thunderbird starts looking for its directories, it is still looking for /data/home/username/.thunderbird.
Solution: First, thunderbird must be uninstalled. Secondly delete all configuration files for thunderbird under /home/username/.thunderbird. Third, reinstall thunderbird and reconfigure.
`sudo pkg remove thunderbird`
`sudo rm -r /home/username/.thunderbird`
`sudo pkg install thunderbird`
The uninstall/reinstall thing might not be necessary, but I wanted to start with a clean slate and not risk any config files left over in some directory I don’t know about. After reinstall, I configured my yahoo account and it connected immediately.
SOLVED.