TBH, I used to hate Firefox's performance, because even loading Facebook froze the entire browser for several msecs (enough to be perceptible), but recently I turned e10s[1] on and the browser feels almost as responsive as Chrome now.
The documentation seems to be outdated, there seems to be an A/B testing right now, and it's recommended to turn off some extensions[2], but this is how I forced e10s to be turned on in `about:config` in the beta:
{
e10s.rollout.cohort: "control",
e10s.rollout.cohortSample: 78,
extensions.e10sBlockedByAddons: false
}