They do not.

[edit]

If I download the README I can see them in every program on my system except Firefox. I previously had issues with CJK only not displaying in Firefox, so there's probably some workaround specific to it...

[Edit 2] If Firefox uses "Noto Color Emoji" (which Firefox seems to use as fallback for any font that doesn't have Emoji characters; fc-match shows a different result for e.g. :charset=2705) then I get nothing, but if I force a font that has the emoji in it (e.g. FreeSerif) then it renders. Weird.