I'm used to hit the f5 key for reloading page on linux/windows. Is there a way to remap reload page shortcut cmd+r to f5 on mac os?
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 & your new key command
& here is your new menu -