They had to sort of rush it, because they wanted to rush out multiprocess, to stop the bleeding of users (which has very much worked [1]). And then they needed

They had to sort of rush it, because they wanted to rush out multiprocess, to stop the bleeding of users (which has very much worked [1]). And then they needed to follow up with the switch to WebExtensions relatively quickly, so that extension authors wouldn't start porting their extensions to multiprocess and then after that effort have to rewrite their extensions to be WebExtensions-compatible. They wanted extension authors to be able to just directly port to WebExtensions. And I do think that a lot more extension authors would have probably abandoned their projects, if they had just ported to multiprocess and then had to port to WebExtensions. Also, a lot of extensions sort of just continue to function without active maintenance. Those are why it would have just as well been really disruptive to space out multiprocess and WebExtensions by a few years. Then we'd have to start over at 0 extensions twice. [1] Multiprocess was rolled out in Firefox 48, on the 2nd August 2016: http://netmarketshare.com/report.aspx?qprid=1&qpaf=&qpcustom=Firefox&qpcustomb=0&qpsp=200&qpnp=24&qptimeframe=M http://netmarketshare.com/report.aspx?qprid=1&qpaf=&qpcustom...