ff-chrome-folder

Install my chrome folder mods

Enable Profile Customizations - in about:config @ toolkit.legacyUserProfileCustomizations.stylesheets
Now, in about:support, click on the ‘Open Directory’ and then create a folder named ‘chrome’ inside (if it doesn't exist).
Clone/copy this repo's contents into the newly created profile/chrome folder
Relaunch Firefox

Note: relaunching Firefox is required to apply any modifications made to the chrome folder

my changes (topmost) + 4 different snippets copypasta'd

re-add panel title, but without "sidebar icon"
(fullscreen) undo clipping of location/toolbar
"expand" traffic button area (to reveal location bar reliably (w/ :hover))
(fullscreen) remove empty space
(fullscreen) sidebar window element - undo extra padding in #webext-panels-browser
sidebar window inner browser = set same bg as sidebery settings
(fix text collision) move sidebery panel title (if visible) to under/right of traffic button bar

add sidebar Compact Mode (animated collapse) https://github.com/Graklinghunter/Hovertext-Css/blob/main/userChrome.css
add padding (arcfox) https://github.com/use-arcfox/arcfox/blob/main/theme/userChrome.css
hide/show main toolbar when cursor over tabs toolbar, and whenever the focus is inside nav-bar (eg: Command+L) https://github.com/MrOtherGuy/firefox-csshacks/tree/master/chrome/autohide_main_toolbar.css
firefox-vertical-tabs

Note: recommended (but not required) for use with screenhook + a vertical tabs sidebar extension (I use sidebery)

Why use screenhook? (macOS only)

Firefox-specific screenhook features

left-edge of window = sidebar peak
top-edge of window = more consistent window dragging (compensates for userChrome.css w/ auto-reveal location bar (preventing drags)) --++works w/ Rectangle snapping
cmd+shift+T to reopen tabs AND windows (Note: requires BTT bindings (steviaOS keeps track of the order tabs/windows were closed in))