The e10s project actually stated back in 2009. The project was put on hold in 2011 because the architectural changes and add-on compatibility breakage was deeme

The e10s project actually stated back in 2009. The project was put on hold in 2011 because the architectural changes and add-on compatibility breakage was deemed insurmountable. In 2013, the project resumed and has been chugging away since. You can see 2011-2013 pause in the revision history of Mozilla's Electrolysis wiki page: https://wiki.mozilla.org/index.php?title=Electrolysis&offset=&limit=500&action=history https://wiki.mozilla.org/index.php?title=Electrolysis&offset... I made a burndown chart of the e10s bugs in Bugzilla that shows the development progress. The bug high water mark was in 2016 and today at least 2,495 bugs (specifically tagged as e10s related) have been fixed: https://people-mozilla.org/~cpeterson/burndown/burndown.html?tracking-e10s=+&since=2013-01-01 https://people-mozilla.org/~cpeterson/burndown/burndown.html...