Dear Mozilla: you have to realize that making the browser faster is worthless if you break extensions like TabMixPlus which provide critical *usability* features! Usability is always more important than performance. It's essentially a completely different browser without TabMixPlus. I might as well use Chrome. For example, I don't see how anyone can manage having tabs that scroll on one line. Instead of being excited about getting a performance boost, I'm now sad that I may one day have to give up how I've been interacting with a browser for 10+ years. What you should have done is work with the developers of the most popular extensions to help them upgrade *before* releasing backwards-incompatible changes to Firefox. Or else roll in some of the critical features to Firefox itself. I've downgraded to 56.0.2, we'll see how long I can keep that going.