I have no idea how you browse the internet with uBlock Origin. It’s literally unusable to me. It’s free, and you should always have it installed, it’s simply essential.
Because uBlock Origin doesn’t work on all platforms and browsers. Notably, it doesn’t work with Apple’s plugin system, so anyone using Safari or an iOS device cannot use it.
Not really. There’s something called Firefox available and it’s published by Mozilla, but Mozilla has to deal with Apple’s restrictions on web browsers by using the webkit rendering engine and Apple’s proprietary plugin system. So it’s not real Firefox.