The ability to have "Disable top bar stickiness" unchecked and "Hide left navigation" checked is a wonderful feature. It keeps things similar to the way they are now.
With all the space freed up we have room to bring back the Rep to the top bar's avatar. This currently doesn't work for mobile devices with a high pixel density. On my Galaxy S9 with a reported resolution of 2768x1440, I see this in Firefox Mobile: