Downgraded to 56, which I have been perfectly happy with, excepting that the download installs (by default) a nasty little side app called "Mozilla Maintenance", which pushed that stinking turd of an upgrade sans my permission. Scrubbed all things Mozilla before downloading 56 and fixed that nasty insult in the Custom install process.
Those out there who think Firefox is slow need to understand something important: it never was intended to be the browser which is the most secure and quickest out of the box, but it is the best browser hands-down for users who know what they need. You don't have to be a programmer to know what makes a browser efficient and secure (I'm not), you just need to do a little research so that you can identify problems, and then spend time searching the enormous library of Firefox addons, which is perfectly organized and very well thought out. Do this, and you will have a browser which will do exactly what you want it to, when you want it to, plus it will be solid as a fortress.
You will never get anything resembling what I have from competing browser ware, because they are happy to give you a simple and easy setup, with controls more tedious to access should you decide on trying that, while handing over your data to anyone who will pay them. Unfortunately, the old consumer ethic is apparently lost on the CEOs behind Firefox 57, because the way of their competition is exactly where they have taken that new version. What a disgusting mess they have made of it! Most of my addons were disabled by it, the interface is ass-backwards, and I have to use it because 57 won't run my easy-access Clear Recent History addon. The process to clear history through the new menu is twice as convoluted and tedious as in the old menu, and after going through that and hitting "Refresh", the site you're on is still tracking you!
So, I've downgraded, and I've nuked the damned Mozilla Maintenance piece of garbage which upgrades whenever Mozilla wants it to, but Mozilla will likely find new ways to steal my freedom to make use of the old version. This is what I have to deal with, and it's because of all you idiots out there who complain when using a browser which never was intended for you to begin with. Why can't you just keep your crybaby fingers off the keyboard, or go use Chrome or IE?