If you compare it with Chrome it's hard to say. But if you just want to use Firefox (because speed is not everything), the difference between 57 and 56 is huge. I spent 15 minutes just opening sites at random to enjoy the speed :).

On the other hand, the addons took a big hit, most of my addons aren't supported anymore. And it seems that everybody is searching for equivalents, as http://addons.mozilla.org/ seems to throw nginx errors right now.