kitbashing nicer sidebar tabs

I love vertical tabs. Given the -- frankly concerning -- amount of tabs I tend to open, they're a must for me. Thing is, none of the native, non-Chromium options quite fit me. Between Zen & Firefox lacking tree-style tabs, and Waterfox lacking container-synced workspaces, all of the options are a little too lackluster for my needs... So I did the only thing a linux user could -- I kitbashed together a solution. :) I started with Firefox (because Chromium is for traitors), onto which I installed Sidebery -- a feature-rich, highly configurable extension for tree-style sidebar tabs. In there, I set up a workspace for each of my containers, and some rules to auto-organize tabs based on the container they belong to. And, voila: ...yeah okay, that does look a little rough. The native tabs at the top are a little redundant now, and the massive sidebar header is a little... unnecessary. Thankfully, Firefox lets users inspect the browser's UI, and tweak it by adding rules to the userChrome.css…