So. There's a programming language called Rust[1] which Mozilla pushed for and developed (it's now developed by a larger community, though Mozilla is still involved). Among other things, it guarantees freedom from memory safety issues and data races. Both are important here.
Freedom from memory safety issues gets rid of a whole class of security bugs (common in browsers) in one fell swoop. Lack of data races lets one write concurrent code without worrying; without needing to program defensively everywhere. "Fearless Concurrency" is what we call this colloquially, after a blog post with the same name[2].
Fearless Concurrency lets us try ambitious things like making layout parallel. Layout in browsers is the step that takes all the nodes on the page with their hierarchy (the DOM) and computed CSS style, and figures out what goes where. All browsers currently do this in a single threaded way.
Servo[3] is a research project by Mozilla. It's a browser engine[4] which does layout (amongst other things) in parallel. It's written in Rust to make this possible (and to avoid security bugs due to memory safety issues). Webrender is a (succesful!) sub-experiment to see if we can be more like game engines and do as much on the GPU as possible.
Here are a bunch of (non mutually exclusive) ways it can go from here:
- Bits and pieces of Servo's code get uplifted into Firefox/Gecko (Gecko is the browser engine behind Firefox). This is already happening[5] (integrating webrender into Firefox is something being discussed, too). This means that Firefox can get some wins without having to wait for Servo to be completed.
- Servo gets its own UI and is shipped as a new browser. A promising UI being worked on is browser.html[6].
- Servo becomes an embedding thingy to be used like a webview.
- Servo replaces Gecko for Firefox for Android: Whilst replacing Gecko in Firefox Desktop is rather hard (the two are tightly intertwined), this is less of a problem in the Android app. It's possible that Servo would have its own app that's either released under a new name or branded as the new Firefox for Android.
- Servo replaces Gecko within Firefox: Hard (not impossible). Probably won't happen.
[1]: http://rust-lang.org
[2]: http://blog.rust-lang.org/2015/04/10/Fearless-Concurrency.ht...
[3]: http://servo.org
[4]: This is not the same thing as a browser. A browser engine handles the displaying and interaction of a given webpage, but doesn't bother itself with concerns like a URL bar, bookmarks, history, a proper UI, etc.