In about:config (see http://kb.mozillazine.org/About:config to learn how to use "about:config")
Set browser.tabs.remote.autostart
to true
Restart Firefox.
Open Activity MonitorOn your next restart, youe10s should see two process "Firefox"be active. To verify that it is active, go to about:support and "Firefox web content"look for a number higher than 0 in "Multiprocess Windows".