Mozilla, the open-source creators of Firefox and Thunderbird, have announced that their Servo project will reach public alpha in June. Nightly builds will be available, presumably around that time, for Linux, OSX, Windows, and Android. Servo is a browser engine that is built in Rust, which emphasizes security and high performance (especially in multi-threaded scenarios).
The technology is really interesting, although it is still quite early. Web browsers are massively single-threaded by design, which limits their potential performance as CPUs widen in core count but stagnate in per-thread performance. This is especially true in mobile, which is why Samsung has been collaborating on Servo for almost all of its life.
Rust, being so strict about memory access, also has the advantage of security and memory management. It is designed in such a way that it's easier for the compiler to know, at compile time, whether you will be trying to access data that is no longer available. The trade-off is that it's harder to program, because if your code isn't robust enough, the compiler just won't accept it. This is beneficial for web browsers, though, because basically everything they access is untrusted, third-party data. It's better to fight your compiler than to fight people trying to exploit your users.
Again, it's still a way off, though. It might be good for web developers to keep an eye on, though, in case any of their optimizations implement standards either correctly, but differently from other browsers and highlights a bug in your website, or incorrectly, which exposes a bug in Servo. Making a web browser is immensely difficult.