Electrolysis development started in 2009. It was enabled by default in Developer Edition starting with Firefox 42 (2015/08/11) and opt-in before that. Nobody k

Electrolysis development started in 2009. It was enabled by default in Developer Edition starting with Firefox 42 (2015/08/11) and opt-in before that. Nobody knew in August 2015 that Mozilla would delay the Electrolysis rollout, allow incompatible extensions would continue working into 2017, pick an arbitrary date to drop XUL extensions instead of tying it to WebExtensions milestones, drop the Add-on SDK at the same time, and not really support gradual porting.