I have two main computers. One has for continuity reasons the old version of Firefox, the other the new one. The old version is so much more usable that I find myself using that computer much more frequently. It is rock solid with 100's of tabs open, all my extensions work and without silly restrictions on what they can and can not do and it uses a lot less memory. It's measurably faster too. I'm all for progress and…
I've also got a Firefox 52 installation lying around and the new version is noticably faster.