thanks to @yhancik I learned about the firefox font inspector and can report that on Debian GNU/Linux 11 (bullseye), Gnome Version 3.38.5, Wayland, running Firefox 91.13.0esr these emojis are being displayed by the following fonts:
Roboto Regular: ꙮ ᵮ ⁂ ∞
DejaVu Sans: ❆ ⨕ ⛢
FreeSans: ꖜ
Noto Sans Bamum Regular: 𖡦
Emoji / Mastodon renders as image: 🕸️
@liaizon @yhancik
Are you referring to this AddOn?
https://addons.mozilla.org/en-US/firefox/addon/font-inspector-webextension/
I hesitate to install it because most people seem to hate it.