Great stuff I use this on all my machines.
Thank you very much NoTabsGuy!
Works very well with i3's tabbed containers.
I also use this little selector in my userChrome.css to visually disable the taskbar, and reconquer a little real-estate of my screen:

#TabsToolbar {
visibility: collapse !important;
}

Excellent !
Used with this userChrome.css to hide tab bar : https://medium.com/@Aenon/firefox-hide-native-tabs-and-titlebar-f0b00bdbb88b

One thing though : with Firefox 75, I can not access to Customize section...

Exactly what I need to stop my tab overload addiction...

Great Add-on !