Kinda found a way to make this work. And it's ugly.

`<alias><family>Noto Color Emoji</family><prefer><family>Noto Sans</family></prefer></alias>`

Basically "If you're going to use Noto Color Emoji, try Noto Sans first, THEN try Emoji".

Good: Seems to stop the emoji numbers (because Noto Sans has those glyphs)
Bad: Overrides it for EVERYTHING (not just Firefox)
Also bad: Forces sans serif, even if the site uses a serif font in the list _after_ the emoji font.

#FontConfig #UglyHacks

Okay, I tricked them. Created a php file that calls php on the updater script with the required flags (update once).
Now I just have to call the web page / script externally via a cron service.
#uglyhacks