Not having slowdowns like you, nor tabs crashing. Reminds me of when Chrome first came out, I ditched Firefox, till I realized Chrome didn't have proper adblocking, and when they did it was awful compared to Firefox's adblocker. It's improved since, but I'm not interested in Chrome since. Firefox has only gotten better and better for me. I guess everyone will experience the new versions differently.
I've been a long time user of Firefox, and after v55, I've been incredibly pleased with the improvements in tab handling (I'm one of those imbeciles who often has hundreds and hundreds of tabs open) and browser performance overall. Like you, I haven't had any stability issues, and the overall resource use is still far lower than Chrome/Chromium/derivatives (like Brave). I'm somewhat disappointed with the removal of the old XUL API and the death of many extensions, but expecting this, I trimmed what I had installed to an absolute minimum. So far so good; can't say I'm really missing anything except maybe Session Manager.
I do have some empathy for your parent comment: I'm not particularly fond of NoScript v10's UI either, if that's their chief complaint. It's different and somewhat cartoonish, but I don't know if my reaction is because of the stylistic changes or the fact that it just changed.
Regardless, Raymond Hill released a version of uMatrix for Firefox 57 which I feel has somewhat more power than NoScript in certain areas (selectively blocking cookies is a nice addition), and I like the UI better. It's not as intuitive, arguably, as the original NoScript, but it's information-dense and provides a fantastic picture of what's going on--better than NoScript ever did.
