someone made a very pretty #transgender firefox icon. I shared it in the pride channel at work, and someone was like "OMG would totally change my icon if i could" and i was like... "You can!" but it required a few steps of prep (like making an icns file of it).
ICONS FILE HERE: https://masukomi.org/misc/trans_firefox_icon.icns
Instructions on how to replace the icon on macOS in 2nd attached image
related to that i wrote a bash script that'll convert any 1024x1024 png into an .icns file for you to customize your icons with too.
https://github.com/masukomi/masuconfigs/blob/master/bin/iconset_maker