In the nightly builds, HTML5 is now native, along with inline SVG and MathML. HTML5 had to be turned on in about:config before but now is on by default. The new parser replaces the original HTML one which has been around since the '90s.
In other news, there will be no v3.7 but the next release will be v4.0. "Process-per-tab" will be turned on in v3.6.5, due this month.