I tried Tree-style tabs and Sidebery, and I bounced off of both. The new native vertical tabs feature works for me, and it is the most impactful feature they've shipped in years for my particular firefox experience.
To me, what they shipped seemed lacking in features to both, with no real improvements.
One other feature that is nice for me is the ability to collapse the sidebar to just the tab icons. It's a nice middle ground between being able to see what I have open and getting a full screen experience.
TST and Sidebery are both fantastic extensions, I don't think they do anything wrong. For whatever reason though, the FF native implementation worked for me where they didn't
cd $FIREFOX_PROFILE_DIR
cd chrome
git clone https://github.com/MrOtherGuy/firefox-csshacks
touch userChrome.css
@import url('firefox-csshacks/chrome/hide_tabs_toolbar.css');
@import url('firefox-csshacks/chrome/window_control_placeholder_support.css');