Please consider adding support for both custom and standard macOS Keyboard Shortcuts. For reference, "Keyboard Shortcuts" or "App Shortcuts" is a system preference on macOS that allows you to add your own window shortcuts like moving an active window such as Firefox to the left or right of the screen. It is not a static list and may change at anytime. Different apps may have different shortcuts.
At the moment, Firefox seems to be the only mainstream browser that doesn't support this. The only shortcuts in Firefox for Mac is currently hardcoded to "Minimize" and "Zoom" it seems like, which makes it impossible to setup simple keybindings for e.g moving the current active Firefox window to the left or right of your monitor.