Command (⌘) as primary modifier. All standard browsing shortcuts use Command where a Windows user would use Ctrl. The action is the same; only the key differs.
F-key behavior on Mac. macOS maps F-keys to system functions (brightness, volume, Mission Control) by default. Bare F-key shortcuts in Firefox require holding Fn unless you've changed the F-key behavior in System Settings → Keyboard. Most Firefox-on-Mac shortcuts use Command combinations instead.
Reader View on Mac. Reader View can be entered from the address bar or with a keyboard shortcut when the feature is available for a page. Once in Reader View, text size, font, line spacing, and narration have their own keyboard controls.
Firefox Developer Tools on Mac. Firefox's developer tools open with a keyboard shortcut using Command and Option. The tools have their own shortcut set for panel navigation, Inspector, Console, Network, Debugger, and others, which is covered in the table above. These differ from Chrome DevTools shortcuts.
Picture-in-Picture. Firefox's picture-in-picture video feature is accessible by keyboard on macOS. Once a video is in the floating window, playback controls have keyboard shortcuts.