At long last, Firefox is going multi-process. Barring an eleventh-hour mishap, Electrolysis (e10s) is coming to the masses with Firefox 48. In the words of long-time Mozillan Asa Dotzler, this is the most significant Firefox change the foundation has ever shipped.
Back in July 2015, Firefox's director of engineering Dave Camp said that some major changes were on their way, with the hope of winning back users and developers. Firefox's market share has been flat or declining since 2010, when Chrome began making major inroads. Finally getting e10s out the door (it was first announced in 2009!) was listed as one of Camp's priorities, along with accelerating the retirement of XUL and XBL.
Mozilla has been trialling Electrolysis to small groups of beta users since December 2015. In Firefox 48, which should be entering beta later today, e10s will be available to all users. Assuming no game-breaking issues are found, the stable build of Firefox 48 will be released to the public with e10s enabled in six weeks (around August 2).
Even when Electrolysis is finally released into the wild, though, Mozilla will be exceedingly cautious with the ramp-up. At first, e10s will only be enabled for a small portion of Firefox's 500 million-odd users, just to make sure that everything is working as intended. Windows XP users, users with screen readers, right-to-left users, and people using add-ons will all be excluded from the initial e10s roll-out.
"Assuming all is well, we’ll turn the knobs so that the rest of the eligible Firefox users get updated to e10s over the following weeks," says Dotzler on his blog. "If we run into issues, we can slow the roll-out, pause it, or even disable e10s for those who got it. We have all the knobs."
The initial version of e10s will split Firefox in twain, dividing the browser between a UI process and a content process. In short, this means that gnarly websites that hog your CPU won't cause the entire browser to become unresponsive. Dotzler says the next step is per-tab processes (so one website running out of control doesn't affect the rest of your tabs), followed by sandboxing for security and then isolating add-ons into their own processes. Mozilla's goal is for this to all happen before the end of 2016.
Firefox 48 beta should be available to download later today (you can already get it directly from the Mozilla FTP server, but the company prefers we not directly link there). In the meantime, you can force-enable Electrolysis in Firefox 47 beta by visiting about:config and then changing the value of browser.tabs.remote.autostart to true. After restarting the browser, you can check whether it's enabled by visiting about:support and checking that "Multiprocess Windows" = 1.