Firefox has become very cluttered, it would be nice if there were an easy way to turn off all the distractions like 'firefox view" and "tab manager" and "profile" and "pocket" and all the other extraneous crap that isn't needed for a basic web experience.
Ergonomics research suggests that reducing clutter makes the interface more clearly understandable, reducing stress, decreasing mistakes and increasing productivity.
From a marketing perspective a more honed browser would be like a return to Firefox's roots