100% this. Folks used to lament Firefox for being slow. And for me it would freeze for seconds sometimes, because of synchronous extensions APIs. Removing XPCO

100% this. Folks used to lament Firefox for being slow. And for me it would freeze for seconds sometimes, because of synchronous extensions APIs. Removing XPCOM, switching to multiprocess, and switching to asynchronous Web Extensions was absolutely vital technologically. Perf is good now.