The Firefox guys are working on a new project called Electrolysis for separating Firefox into multiple processes, like Chrome. This has been my #1 feature request for Firefox for quite some time, and now they’ve got their proof of concept running. Considering the size and age of the Gecko code, though, I won’t be holding my breath quite yet.
Electrolysis: Separating Firefox
This post is over ten years old. Chances are, I've learned enough to have advanced my thinking about some of this stuff.