I recently upgraded from firefox 55 to firefox 58 nightly and many extensions have to be updated. Treestyletabs is the only extension that I really use and it has been reimplemented as a sidebar panel. The difference is that it now has a giant bar at the top like this:
saying in really big letters Tree Style Tab. I was able to eliminate the tabs at the top of the screen by adding
#tabbrowser-tabs { visibility: collapse !important; }
to my .mozilla/firefox/???/chrome/userChrome.css
file. I want to know if there is something similiar I can do to hide the sidebar panel header while still keeping the sidebar panel.