What is it supposed to do?
There is no mention of F9 on this support page either:
https://support.mozilla.org/en-US/kb/keyboard-shortcuts-perf...
Am I missing something?
F9 on Windows
Ctrl + Alt + R on Linux
Command + Option + R on macOS
(It uses JS to only show the one for your platform but with view source you can see it mentions all three of these different OSes.)
So I guess the first guy is a Windows user and you other two use Linux.
There is a dropdown at the top-right to select the platform - no need to view source.