Karey: you need Firefox 56 ESR and version 31.2.3 https://addons.mozilla.org/en-US/firefox/addon/colorfultabs/versions/31.2.3
After installing colorful tabs, go to add-ons > colorful tabs > disable updates.
Legacy AddOns fixed to work on current versions of Firefox and lots of awesome goodies!
Karey: you need Firefox 56 ESR and version 31.2.3 https://addons.mozilla.org/en-US/firefox/addon/colorfultabs/versions/31.2.3
After installing colorful tabs, go to add-ons > colorful tabs > disable updates.