userChrome.css

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");

:root {
  --tab-max-height: 10px !important;
}

.tabbrowser-tab .tab-label {
    font-size: 12px !important;
}

.tabbrowser-tab .tab-loading-burst {
  display: none !important;
}

.tabbrowser-tab .tab-close-button {
  visibility: collapse !important;
}

.titlebar-min, .titlebar-max,
.titlebar-restore, .titlebar-close {
  display: none !important;
}

.tabbrowser-tab:not([style^="max-width"]):not([pinned]),
.tabbrowser-tab[style^="max-width: 100px !important;"]:not([pinned]) {
	max-width: 100% !important;
}

.tabbrowser-tab:not([style^="max-width"]):not([pinned]):not([fadein]),
.tabbrowser-tab[style^="max-width: 100px !important;"]:not([pinned]):not([fadein]) {
	max-width: .1px !important;
}

#TabsToolbar .titlebar-spacer {
	display: none !important;
}

.tabbrowser-tab[usercontextid]>.tab-stack>.tab-background>.tab-bottom-line {
	display: none;
}

#tabs-newtab-button {
  display: none !important;
}

#back-button, #forward-button {
  display: none !important;
}

.tab-label {
  text-align: center !important;
  margin-left: auto !important;
  margin-right: auto !important;
}

.tab-icon-stack {
  display: none !important;
}

#PanelUI-button {
  -moz-box-ordinal-group: 0 !important;
  order: -1 !important;
  margin-right: 8px !important;
}

#tabbrowser-tabs,
#tabbrowser-tabs > #tabbrowser-arrowscrollbox,
.tabbrowser-tabs .tabbrowser-tab {
  min-height: var(--tab-min-height) !important;
  max-height: var(--tab-min-height) !important;
}

#TabsToolbar {
  height: var(--tab-min-height) !important;
  margin-top: -8px !important;
  margin-bottom: -1px !important;
  margin-right: -1px !important;
  margin-left: -1px !important;
}

#TabsToolbar .tabbrowser-tab[selected="true"] .tab-label {
    font-weight: 700 !important;
}

#TabsToolbar .tab-label {
    font-family: "0xProto Nerd Font" !important;
}

#toolbar-menubar {
  background-color: #11111b !important;
  color: #cdd6f4 !important;
}

menupopup, popup, panel {
  --panel-background: #11111b !important;
  --panel-color: #cdd6f4 !important;
}

menupopup > menuitem:hover, menupopup > menuitem[selected="true"],
menupopup > menu:hover, menupopup > menu[selected="true"] {
  background-color: #313244 !important;
  color: #cdd6f4 !important;
}

/* Source file https://github.com/MrOtherGuy/firefox-csshacks/tree/master/chrome/autohide_main_toolbar.css made available under Mozilla Public License v. 2.0
See the above repository for updates as well as full license text. */

/* This style hides the main toolbar and shows it when the cursor is over the tabs toolbar as well as whenever the focus is inside nav-bar, such as when urlbar is focused. */

:root{
  --uc-navbar-transform: -40px;
  --uc-autohide-toolbar-delay: 1.8s;
  --uc-autohide-toolbar-duration: 400ms;
}
:root[uidensity="compact"]{ --uc-navbar-transform: -34px }

#navigator-toolbox > div{ display: contents; }
:root[sessionrestored] :where(#nav-bar,#PersonalToolbar,#tab-notification-deck,.global-notificationbox,#notifications-toolbar){
  transform: translateY(var(--uc-navbar-transform))
}
:root:is([customizing],[chromehidden*="toolbar"]) :where(#nav-bar,#PersonalToolbar,#tab-notification-deck,.global-notificationbox,#notifications-toolbar){
  transform: none !important;
  opacity: 1 !important;
}

#nav-bar:not([customizing]){
  opacity: 0;
  transition:  transform var(--uc-autohide-toolbar-duration) ease var(--uc-autohide-toolbar-delay), opacity var(--uc-autohide-toolbar-duration) ease var(--uc-autohide-toolbar-delay) !important;
  position: relative;
  z-index: 2;
}
#titlebar{ position: relative; z-index: 3 }

#navigator-toolbox,
#sidebar-box,
#sidebar-main,
#sidebar-splitter,
#tabbrowser-tabbox{
  z-index: auto !important;
}
/* Show when toolbox is focused, like when urlbar has received focus */
#navigator-toolbox:focus-within > .browser-toolbar{
  transform: translateY(0);
  opacity: 1;
  transition-duration: var(--uc-autohide-toolbar-duration), var(--uc-autohide-toolbar-duration) !important;
  transition-delay: 0s !important;
}
/* Show when toolbox is hovered */
#titlebar:hover ~ .browser-toolbar,
.browser-titlebar:hover ~ :is(#nav-bar,#PersonalToolbar),
#nav-bar:hover,
#nav-bar:hover + #PersonalToolbar{
  transform: translateY(0);
  opacity: 1;
  transition-duration: var(--uc-autohide-toolbar-duration), var(--uc-autohide-toolbar-duration) !important;
  transition-delay: 0s !important;
}
:root[sessionrestored] #urlbar[popover]{
  opacity: 0;
  pointer-events: none;
  transition: transform var(--uc-autohide-toolbar-duration) ease var(--uc-autohide-toolbar-delay), opacity var(--uc-autohide-toolbar-duration) ease var(--uc-autohide-toolbar-delay);
  transform: translateY(var(--uc-navbar-transform));
}
#mainPopupSet:has(> [panelopen]:not(#ask-chat-shortcuts,#selection-shortcut-action-panel,#chat-shortcuts-options-panel,#tab-preview-panel)) ~ toolbox #urlbar[popover],
.browser-titlebar:is(:hover,:focus-within) ~ #nav-bar #urlbar[popover],
#nav-bar:is(:hover,:focus-within) #urlbar[popover],
#urlbar-container > #urlbar[popover]:is([focused],[open]){
  opacity: 1;
  pointer-events: auto;
  transition-delay: 0ms;
  transform: translateY(0);
}
#urlbar-container > #urlbar[popover]:is([focused],[open]){
 transition-duration: 100ms; /* Faster when focused */
}
/* This ruleset is separate, because not having :has support breaks other selectors as well */
#mainPopupSet:has(> [panelopen]:not(#ask-chat-shortcuts,#selection-shortcut-action-panel,#chat-shortcuts-options-panel,#tab-preview-panel)) ~ #navigator-toolbox > .browser-toolbar{
  transition-delay: 33ms !important;
  transform: translateY(0);
  opacity: 1;
}
/* If tabs are in sidebar then nav-bar doesn't normally have its own background - so we nee to add it back */
#nav-bar.browser-titlebar{
  background: inherit;
}
#toolbar-menubar:not([autohide="true"]) ~ #nav-bar.browser-titlebar{
  background-position-y: -28px; /* best guess, could vary */
  border-top: none !important;
}

/* Bookmarks toolbar needs so extra rules */
#PersonalToolbar{ transition: transform var(--uc-autohide-toolbar-duration) ease var(--uc-autohide-toolbar-delay) !important; position: relative; z-index: 1 }

/* Move up the content view */
:root[sessionrestored]:not([chromehidden~="toolbar"]) > body > #browser{
  margin-top: var(--uc-navbar-transform);
}
@media -moz-pref("browser.fullscreen.autohide"),
  (-moz-bool-pref: "browser.fullscreen.autohide"){
  :root[sessionrestored][sizemode="fullscreen"] > body > #browser{
    margin-top: revert;
  }
}