A quick summary on how to get my old Fedora 12 to display Emojis when browsing the web (Instagram, for example).
Download the EmojiOneColor font from its Github repo.
Untar the bundle. Don’t run the installation script (maybe it works, but I prefer messing up things myself).
Create a directory named “emoji” (or any other name) in /usr/share/fonts/ and copy EmojiOneColor-SVGinOT.ttf into that directory.
Clear the font cache (as root):
# fc-cache -f
Find Emoji One as a listed font (non-root):
$ fc-list | grep -i emoji Emoji One Color:style=Regular
That’s it, on my machine. There was no need to add a font configuration script: After restarting Firefox and Google Chrome, both started displaying Emojis instead of those empty boxes (Chrome shows them only in black and white, Firefox in color).
A font configuration file is needed if the browser sticks to the text font even for Emoji characters, ending up with rubbish or empty boxes. In this case, the font configuration file is required to set the Emoji font as default, and fall back on text fonts. All this according to the comments in the bundle I downloaded — I didn’t need this myself, so why mess with the fonts settings?