firefox mac os: how to remap cmd+r to f5?
You can remap any shortcut on macOS - so long as the item you wish to change has a Menu entry.

To demonstrate on Safari - I don't have Firefox..

Original menu - 



So, to change it - System Preferences > Keyboard > Shortcuts >App Shortcuts
Click the + button, set your required app, the menu exact name &amp; your new key command



&amp; here is your new menu -