facebook-oatmeal-icons-firefox
Replace Facebook like icons with icons created by The Oatmeal (https://imgur.com/a/EzbrM)
License
The code is available under GPL.
The images are not under a specific license but the author allows all uses: "If anyone wants to use them they're all yours, no credit needed." (https://www.facebook.com/theoatmeal/photos/a.10150413121115078.628758.220779885077/10156614705980078/})