You have the source code and can create a build that works like that. The current way it works, which is with a whitelist, makes it a lot harder for some malwar

You have the source code and can create a build that works like that. The current way it works, which is with a whitelist, makes it a lot harder for some malware to exist and hijack a protocol and this is, in my opinion, a good thing. Remember that Firefox is used by millions, and a whitelist is a measure that adds a bit more safety to the millions out there that are not as tech-savvy as you and still want to browse the web.