But it still doesn't seem to work on GitHub, did you whitelist GitHub for the preventDefault or is GitHub just a bit extra when it comes to hijacking keybinds?
Ah bummers, but nonetheless thanks for implementing this feature!
EDIT: I just took a look at GitHub's source code, and they mentioned a setting to turn off these shortcuts, and it really exists!! Under https://github.com/settings/accessibility one can turn off, all "Character keys" which means shortcuts without a modifier. I've never used them, so I just disabled it, and now forward slash always opens the Firefox search :0