Earlier quoted context omitted.
People still seem to make the statement that Firefox uses more RAM, when in fact, since Firefox 20, it has consistently used LESS ram than all the other browsers. I have 40 tabs open now, and it's using 1.16 GB which is awesome. I actually want it to take up more because I have 6GB of free RAM not being used, which is a waste. Compare that to chrome. Using the same number of tabs and it can easily take up more than 3…
Here is a link to the project https://wiki.mozilla.org/Electrolysis . The only thing about using separate processes is that you increase memory usage, since every tab has overhead, and tabs can't share resources (chrome tends to go process per domain).
bang, you have multiprocess firefox.
a word of warning: it doesn't work so well, so i guess it's experimetal. you'll probably want to revert to false ;-)