Servo is a research project, not a project to bring multiprocess support to Gecko. (Presumably you mean multiprocess support, not multithreading—Gecko is already highly multithreaded.)

In any case, Gecko is multiprocess already, and it's fully deployed on Firefox OS (and, as of recently, sandboxed). Firefox is not multiprocess because (generally) the front end has not yet been ported, and the project to do that is called Electrolysis.

Both are under implementation. Servo is nowhere near ready yet as would be expected for a totally new engine (although it is making progress [1]). Electrolysis is in for Firefox Mobile / Firefox OS and is in progress for desktop[2].

[1] https://twitter.com/metajack/status/364571230331875331

[2] https://wiki.mozilla.org/Electrolysis

Some more screenshots from Servo: http://about-rust.blogspot.de/2013/08/some-pages-in-servo-as...

On the topic of the HTML parser, you may be interested in https://developer.mozilla.org/en-US/docs/Mozilla/Gecko/HTML_...

See https://wiki.mozilla.org/Platform/GFX/OffMainThreadCompositi...

That's single threaded compositing on its own thread.

Which is a step in the right direction. After that they can make it multithreaded. Right now it's all too tied together.