WebRTC is now a web standard and ships in multiple browsers. If you consider such technology to be outside the scope of a browser, then you're going to need to convince a whole lot of people.
The complaint is not about WebRTC, but about Hello.
The comments in this thread are going in loops.
"Hello shouldn't be bundled with a browser."
"But it is just a small wrapper around WebRTC."
"Yeah, but it's out of scope for the browser."
"WebRTC is a web-standard"
Mozilla's mission is to promote openness, innovation & opportunity on the Web. There's nothing specific about browsers in the mission, though it is used to help further the mission.
If you take that into context when you look at Hello, you can see why the organization might want to leverage the Firefox user base to introduce something with negligible overhead (Hello) that would help to advance that mission.
