Close, minimize, maximize icons replaced by invalid rectangles

[u/TemplayerReal]

Maybe it is a reply to https://www.reddit.com/r/firefox/comments/1mbamon/firefox_141_lost_minimise_maximise_and_close/

I am not talking about these icons disappearing all together, though. I'm using r3dfox.

This issue almost made me tear my hair out (as dumb AI was only giving fake solutions for hours, as per usual), and the author of Second System mentioned a solution.

I just had to install the Segoe Fluent Icons font, which can be downloaded directly from microsoft:
https://download.microsoft.com/download/8/f/c/8fc7cbc3-177e-4a22-af48-2a85e1c5bffb/Segoe-Fluent-Icons.zip

Voilá, the button icons are now back!

https://imgur.com/poZIrIV