I kind of think the opposite. A browser is probably the most technically challenging and complicated project out there, if you can't deal with dependencies then

I kind of think the opposite. A browser is probably the most technically challenging and complicated project out there, if you can't deal with dependencies then chances are your code will not be of sufficient quality to make it into the project that still makes up the whole. However, if it's split into a lot of dependencies then it's much more accessible because you can contribute to a smaller and more easily understood project. In this case it looks like you can contribute to one of the servo project packages and those changes will make it downstream into Firefox, that's great as Servo has a (relatively) small and easily understood code base!