sudo apt-get install fonts-symbola worked for me!
fonts-symbola worked for me as well.
I’m curious why this isn’t the default? It’s less that 3M installed, and this is exactly the kind of thing that makes users feel that Linux/Open Source is “not ready for prime time.”
Came here to report the same issue. I faced this just after making a clean install of UbuntuMATE 18.04 and using Thunderbird. @DougBarton is right, fonts-symbola should be installed on the distro by default to provide a cleaner experience out of the box.
What if you install via snap? sudo snap install thunderbird