That's great that you've fostered a love for reading, I believe that's an incredibly important thing for a young mind.
But i also don't think not allowing video games at all isn't necessary. I grew up reading and playing online games, it's possible to ensure a balance. And today online games are a huge part of the socializing that happens. It sucks to sit at the lunch table and have your friends talk about conversations they had that you couldn't be a part of.
I was curious as well so I looked at the git tree. I'm not familiar with Firefox code, but I'm assuming I found the list:
From here
So it looks like it's mostly to do with the account system of Firefox. I'm not sure why their websites would need special protection, but whatever. It's not malicious, for now