I wonder to what extent that helps prevent malware from installing a malicious addon to Firefox, because by using the same mechanism as cheating in video games,

I wonder to what extent that helps prevent malware from installing a malicious addon to Firefox, because by using the same mechanism as cheating in video games, you can hot-patch a running browser process to disable the functionality to keep it from installing unsigned addons. Technically, in Windows you would just call WriteProcessMemory to modify memory content of another process.