how exactly did you remove them ? a proper:
sudo snap remove <snapname>should trigger systemd to remove all remaining units for services and mounts shipped by the respective snaps (along with a good bunch of other things that were auto-generated by systemd, apparmor_parser and other system utilities when you install them or connect an interface) …
Yes, I used that command. If I recall correctly, I removed the hunspell snap first so perhaps that prevented the firefox snap from noticing the hunspell mount? If I have time later I’ll try to duplicate the issue before posting a bug report.