Try to create a new profile to compare nondestructively: "firefox --ProfileManager" I can confirm both that newer firefox is notably more responsive than old,

Try to create a new profile to compare nondestructively: "firefox --ProfileManager" I can confirm both that newer firefox is notably more responsive than old, and that I (or an extension, though I don't have many) managed to get a ff profile into a state where it had inexplicably bad performance, esp. unpredictable long freezes.