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: 🕸️