How to disable colored emoji font in Firefox?

Firefox 50's release notes:

Emoji for everyone! Firefox will use built-in Emoji on operating systems without native Emoji fonts (Windows 8.0 and lower and Linux)

So I'm on Windows 7 and I absolutely dislike colored emoji for how much distracting they are. There is no font file called "EmojiOne Mozilla" to delete from Windows' fonts folder, unfortunately. And there is no relevant option in about:config list I could find.

How do I disable colored emoticons?

Solution 1:

It's not installed as a system font. The font file is contained within the Firefox directory, and deleting that one is sufficient. Note that you'll need to actually delete or move the file - simply renaming it, even changing the file extension, is not enough to prevent its use.

In the current Aurora build, the file you'll want to remove is <firefox>\fonts\EmojiOneMozilla.ttf, where <firefox> is the installation folder, which will vary depending on the bit-ness (Program Files or Program Files (x86)) and channel (Mozilla Firefox, Aurora or Nightly). On Windows you can right-click Firefox shortcut and select Open file location.

See also: https://bugzilla.mozilla.org/show_bug.cgi?id=1231701#c135

Solution 2:

Go to about:config, context menu (right click) > new > string. Set font.name-list.serif.x-unicode as preference name and Segoe UI Symbol as string value.
Colored emojis are instantaneously disabled, no need to refresh open tabs or restart the browser.

Source

Solution 3:

This is what I ended up doing for myself: I took the EmojiOneMozilla.ttf font file from <Firefox installation folder>\browser\fonts\ and edited all its emoji symbols to contain the "not defined" symbol at the very end of the Unicode range.

Using FontForge editor, I copied it and pasted over all the emoji symbols (edit > select > glyphs worth outputting), and installed it as a system font, and gave it a unique name so it could be used in Firefox as a custom installed font (as described in the other answer here) and now every emoji symbol is a square.

You could use an empty space symbol instead if you want, but then you won't be able to see where an emoji is expected to be, and it might be a bit confusing.