Electrolysis ("e10s") has been enabled by default on the Nightly and Developer Edition* channels, if you'd like to help test it.
* Although we're currently running an A/B test to measure performance differences with e10s enabled and disabled, so you might fall into the disabled cohort when you run Dev Edition. This experiment is scheduled to end in a few days.
The last time I tried Electrolysis I had issues with plugins. Some of the plugins are fairly essential to me (e.g. NoScript, HTTPS Everywhere) so I wasn't able to use it as a daily driver. The fault for that may rest at the plugin developers, but I wonder if it has been resolved?
It's still imperfect; expect some breakage, depending on your addons. I myself faced problems in HighlightAll (fixed in recently-released 1.8), and VimFx (still broken, which leads me to disable e10s for now).
Nit: you mean (js-based) addons/extensions, not (binary) plugins.