Earlier quoted context omitted.
Sideberry for Firefox has settings that allow changing how new tabs behave. One of the settings allows placing new tabs on top of the list.
It seems Sideberry only allows opening new tabs at the beginning of the list. That is not the same as just sorting newest at the top, since it also switches the order of native tabs as well. I want native tabs (since we can't hide them) to remain left to right. And I can't even move the "New Tab" button to the top.
zen also has a "compact mode" than hides the native tabs, but it hides other things you might want as well