Whenever I raised issues with Mozilla about things that degraded, it was always either talking to a brick wall or a wontfix. They made the decision based on one person complaining about it being the old way, implemented the change, and no matter that other people liked the old way, it wouldn't be changed back or made configurable.
I then tried to compile Firefox for Android myself and cherry pick only security updates, but that was enough of a pain in the ass that I gave up on it.
And before you mention it, changing default font size in browser/OS doesn't really help, mostly makes things worse (Bad categories like "medium", "huge" instead of font size, page layouts breaking etc.)
The newest version mentioned in this article actually feels faster than chrome although I'm not crazy about the new ui it is usable without difficultly and a work in progress.
Experiences from years ago aren't really relevant any more, as Firefox has gotten a lot of work done the last couple of years.
But then, I also didn't think 57 for desktop was a big update. For me, it made zero speed difference (Firefox has always been fast on my laptop), on Linux with vertical tabs there is almost zero UI difference, and the only new thing was having to throw out all add-ons with the bathwater. Somehow, it seems I always experience things differently from other people.
Will it be continually "improving" when they drop extension support?