I tried out the Tree-Style Tab extension and got everything configured and working nicely but I was left with both the Firefox tab bar and the Tree-Style Tab sidebar on-screen at the same time. I tried to find a way to hide Firefox's tab bar while the Tree-Style Tab sidebar is on-screen (Which is what I want to happen) but only found one superuser thread saying I need to adjust some esoteric file deep within Firefox's app files called "userChrome.css".
This ought to be a one-button fix otherwise Mozilla's "recommendation" of Tree-Style Tab for the modern Firefox browser seems half-hearted at best. I understand there is perhaps some danger involved in exposing such a setting that a user might end up without tabs of any kind, but surely there could be some opt-in setting to toggle off the default tab bar while the sidebar of a user's selected extension is on-screen or something like that?