Q:

How do I configure the default emoji font to be used system-wide / in OS and Browser? (it's currently Symbola but I want Noto)

I'm running elementary OS 0.4.1 Loki.
The emoji font I want to use system wide (in the OS and in the Browser) is the non-color version of Noto or: NotoEmoji-Regular.ttf (provided by Google)
How do I configure it to be default instead of Symbola (which is the current default) ?

A:

One way to set Noto Emoji as the default emoji font in elementary OS is to setup some local font config files. 
Create the directory and the file itself with:

mkdir -p ~/.config/fontconfig/
touch ~/.config/fontconfig/fonts.conf

And then populate the created file with the following text:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">

<fontconfig>
  <match>
    <test name="family"><string>sans-serif</string></test>
    <edit name="family" mode="prepend" binding="strong">
      <string>Noto Emoji</string>
    </edit>
  </match>
  <match>
    <test name="family"><string>serif</string></test>
    <edit name="family" mode="prepend" binding="strong">
      <string>Noto Emoji</string>
    </edit>
  </match>
  <match>
    <test name="family"><string>monospace</string></test>
    <edit name="family" mode="prepend" binding="strong">
      <string>Noto Emoji</string>
    </edit>
  </match>
  <match>
    <test name="family"><string>Apple Color Emoji</string></test>
    <edit name="family" mode="prepend" binding="strong">
      <string>Noto Emoji</string>
    </edit>
  </match>
</fontconfig>

And finally flush the font cache: fc-cache -f -v.
If Noto is installed you should now see Noto for emoji unicode blocks in the browser for example, and Symbola filling in where Noto is lacking.

