Hiding title bar and tab bar were confugurable before. When you installed tree style tab it automatically made the tab bar hidden at that time. It was the most customizable dev browser.

Then they rewrote the the UI engine replacing XUL and made Firefox a more 'user friendly browser' copying all UI features of chrome sacrificing the customization options.

I am a heretic now who is running Windows 10 with WSL2 and edge as primary browser due the points you mentioned.