Firefox has a much smaller team than Chrome to begin with, and they can only work on so many things. If they keep spending time in "re-inventing the wheel" (in addition to what you listed, they also revamp their mobile client quite a few times in my recent memory), what left behind is attention to details in UX and UI that users can feel, which is what Firefox was famous for.

I'm not a developer, but I've submitted or engaged in many bug tickets on Bugzilla. What I can tell from my experience is that the response to bugs (critical or not) are getting slower and slower. Not just patches, sometimes you will have tickets that took years to have someone even looking at it. My feeling is most of developers are more likely to spend their time on Mozilla's "big goals" than maintenance.

Just to give one example, there is still no full range video support in Firefox in the era of video game streaming. This alone lets me to have to use Chrome to watch Twitch.