I use youtube.com (desktop version) in Mobile Safari and get adblocking without jailbreak.
I prefer the desktop website because it lets me watch the videos in better quality than the mobile website. m.youtube.com seems to limit the maximum bitrate and/or resolution of the videos. Did anyone else notice that?
iOS does not allow "real" alternative web browsers with their own rendering and JavaScript engines, so Firefox on iOS is forced to being little more than rebranded Safari.
No. I never see ads on Youtube on my own devices, and that barely requires any effort.