Google Noto Color Emoji on Arch Linux desktop. Don't forget to remove Firefox's built-in EmojiOne font.

51-noto-color-emoji.conf.xml

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<!-- /etc/fonts/conf.avail/51-noto-color-emoji.conf -->
<fontconfig>
    <selectfont>
        <acceptfont>
            <pattern>
                <patelt name="family"><string>Noto Color Emoji</string></patelt>
            </pattern>
        </acceptfont>
    </selectfont>
    
    <match target="font">
        <test name="family">
            <string>Noto Color Emoji</string>
        </test>
        <edit name="scalable" mode="assign"><bool>true</bool></edit>
        <edit name="embeddedbitmap" mode="assign"><bool>true</bool></edit>
        <edit name="hinting" mode="assign"><bool>true</bool></edit>
        <edit name="hintstyle" mode="assign"><const>hintfull</const></edit>
    </match>

    <!-- Experimental -->
    <match target="pattern">
        <test name="family" qual="first" compare="contains">
            <string>emoji</string>
        </test>
        <edit mode="assign" name="color">
            <bool>true</bool>
        </edit>
        <edit mode="assign" name="family">
            <string>Noto Color Emoji</string>
        </edit>
    </match>

    <match target="pattern">
        <test name="prgname" compare="not_eq">
            <string>java</string>
        </test>
        <edit name="family" mode="prepend">
            <string>Noto Color Emoji</string>
        </edit>
    </match>
</fontconfig>