[pygy_]

For 1) WebRender was developed for Servo and is being ported to Firefox as part of the Quantum effort (Firefox Rustification).

[klibertp]

Is it being rewritten in non-Rust during the porting? Or is it left in Rust, with build system taking care to compile and link it properly?

[tangent128]

It's being left in Rust, yes. Firefox already contains Rust components, such as Stylo.