Comment # 10 on bug 1092737 from Marguerite Su

    <match target="pattern">
      <test qual="any" name="family" compare="eq">
         <string>sans-serif</string> 
      </test>
      <edit name="family" mode="prepend" binding="strong">
         <string>emoji</string>
      </edit>
    </match>

This is the cause.

Noto Color Emoji font will be prepended to sans-serif