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).
i think electrolysis currently does something like grouping tabs like 10 per process or something.
In nightly:
about:config
=> browser.tabs.remote
set to true
restart firefox.
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 ;-)
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).