This would not have protected your father from any of that. If hostile code can inject an extension into your Firefox profile, it can also install a keylogger or read your unencrypted Firefox password store. There is almost no protection against your credentials being exfiltrated. Neither would it protect you against unwanted notifications. It will however greatly reduce the functionality of Firefox.

This is security theater.

> Browser extensions are a powerful, beautiful, dangerous bit of tech. Is it asking too much to put some guard rails in place that really aren’t too much trouble to follow?

There are many layers of guard rails already. The problem is that now they want to also inspect every extension that I use, even if it is for completely private use and will never be available to the public. And Mozilla does not exactly have a good track record with trust.