The biggest challenge with per-tab processes (Firefox's Electrolysis or e10s feature) is maintaining add-on compatibility. Chrome didn't have add-ons at first and didn't need to worry about backwards compatibility (at the time).

Firefox is also working on per-tab event queues to improve UI responsiveness. In the meantime, I recommend Firefox users check out the experimental "Suspend Background Tabs" add-on. Written by the author of Adblock Plus, Suspend Background Tabs will pause JavaScript execution and timers for background tabs.

https://addons.mozilla.org/en-US/firefox/addon/suspend-backg...