The Mozilla announcement explains, "Servo is an attempt to rebuild the Web browser from the ground up on modern hardware, rethinking old assumptions along the way. This means addressing the causes of security vulnerabilities while designing a platform that can fully utilize the performance of tomorrow’s massively parallel hardware to enable new and richer experiences on the Web. To those ends, Servo is written in Rust, a new, safe systems language developed by Mozilla along with a growing community of enthusiasts."
Samsung in particular has been working on bringing the Rust programming language and Servo to Android and the ARM architecture. The code to Servo is developed in the open on GitHub as is Rust.
The Rust programming language has been in development by Mozilla Research for several years and uses LLVM for its back-end. Rust is designed to be a "safe, concurrent, practical language" and has a syntax similar to C/C++. Rust 0.6 was also announced today and brings with it numerous improvements.
Right now Mozilla is using the Gecko engine within Firefox and their other projects, which has begun to show its age against WebKit and others with the rendering engine dating back to the 90's in the Netscape days.
Mozilla says to expect more out of the Rust programming language and the Servo browser engine in the coming years.