userChrome.css

 :root {

   /* Minimal Functional Fox variables*/
  --mff-bg: #292f36;
  --mff-icon-color: #e0fbfc;
  --mff-nav-toolbar-padding: 8px;
  --mff-sidebar-bg: var(--mff-bg);
  --mff-sidebar-color: #e0fbfc;
  --mff-tab-border-radius: 0px;
  --mff-tab-color: #fefefa;
  --mff-tab-font-family: "Cantarell", sans;
  --mff-tab-font-size: 11pt;
  --mff-tab-font-weight: 400;
  --mff-tab-height: 32px;
  --mff-tab-pinned-bg: #70c1b3;
  --mff-tab-selected-bg: #ee6c4d;
  --mff-tab-soundplaying-bg: #9c89b8;
  --mff-urlbar-color: #98c1d9;
  --mff-urlbar-focused-color: #e0fbfc;
  --mff-urlbar-font-family: "Cantarell", serif;
  --mff-urlbar-font-size: 12pt;
  --mff-urlbar-font-weight: 700;
  --mff-urlbar-results-color: #e0fbfc;
  --mff-urlbar-results-font-family: "mononoki Nerd Font", serif;
  --mff-urlbar-results-font-size: 12pt;
  --mff-urlbar-results-font-weight: 700;
  --mff-urlbar-results-url-color: #98c1d9;
  /*   --mff-tab-selected-bg: linear-gradient(90deg, rgba(232,74,95,1) 0%, rgba(255,132,124,1) 50%, rgba(254,206,168,1) 100%); */
  /*   --mff-urlbar-font-weight: 600; */

  /* Overriden Firefox variables*/
  --autocomplete-popup-background: var(--mff-bg) !important;
  --default-arrowpanel-background: var(--mff-bg) !important;
  --default-arrowpanel-color: #fefefa !important;
  --lwt-toolbarbutton-icon-fill: var(--mff-icon-color) !important;
  --panel-disabled-color: #f9f9fa80;
  --toolbar-bgcolor: var(--mff-bg) !important;
  --urlbar-separator-color: transparent !important;
}

/*
  _____ _   ___ ___
 |_   _/_\ | _ ) __|
   | |/ _ \| _ \__ \
   |_/_/ \_\___/___/

*/

.tab-background[selected="true"] {
  background: var(--mff-tab-selected-bg) !important;
}

.tab-background:not[visuallyselected] {
  background: var(--mff-tab-selected-bg) !important;
  opacity: 0.5 !important;
}

/* This positions the tabs under the navaigator container */
#titlebar {
  -moz-box-ordinal-group: 3 !important;
}

.tabbrowser-tab::after,
.tabbrowser-tab::before {
  border-left: none !important;
}

.tab-background {
  border: none !important;
}

.tabbrowser-arrowscrollbox {
  margin-inline-start: 4px !important;
  margin-inline-end: 0px !important;
}

.tab-close-button {
 display: none !important;
}

.tab-text {
  font-family: var(--mff-tab-font-family);
  font-weight: var(--mff-tab-font-weight);
  font-size: var(--mff-tab-font-size) !important;
  color: var(--mff-tab-color);
}

/* Hide the favicon for tabs */
hbox.tab-content .tab-icon-image {
  display: none !important;
}

/* Show the favicon for tabs that are pinned */
hbox.tab-content[pinned=true] .tab-icon-image {
  display: initial !important;
}

hbox.tab-content[pinned=true] .tab-text {
  display: none !important;
}

#tabbrowser-tabs {
  --tab-loading-fill: #033433 !important;

}

.tab-label-container:not([textoverflow]) {
  display: flex;
  overflow: hidden;
  justify-content: center;
width: 50% !important;
  max-width: 50% !important;
  min-width: 50% !important;
}

/* .tab-label-container::after {
  content: "?" !important;

} */

.tab-line {
  display: none !important;
}

.tabbrowser-tab {
  border-radius: var(--mff-tab-border-radius) !important;
  border-width: 0;
  height: var(--mff-tab-height) !important;
  margin-bottom: 4px !important;
  margin-inline-end: 4px !important;
  margin-top: 4px !important;
  max-height: var(--mff-tab-height) !important;
  min-height: var(--mff-tab-height) !important;
}

.tabbrowser-tab[soundplaying="true"] {
  background-color: var(--mff-tab-soundplaying-bg) !important;
}

#tabs-newtab-button {
  list-style-image: url("add.svg") !important;
  opacity: 0.7;
}

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

/*
  _____ ___   ___  _    ___   _   ___
|_   _/ _ \ / _ \| |  | _ ) /_\ | _ \
  | || (_) | (_) | |__| _ \/ _ \|   /
  |_| \___/ \___/|____|___/_/  \_\_|_\
*/

.urlbar-icon > image {
  fill: var(--mff-icon-color) !important;
  color: var(--mff-icon-color) !important;
}

.toolbarbutton-text {
  color: var(--mff-icon-color)  !important;
}
.urlbar-icon {
  color: var(--mff-icon-color)  !important;

}

.toolbarbutton-icon {
/* filter: drop-shadow(0 0 0.75rem crimson); */
}

#urlbar-results {
  font-family: var(--mff-urlbar-results-font-family);
  font-weight: var(--mff-urlbar-results-font-weight);
  font-size: var(--mff-urlbar-results-font-size) !important;
  color: var(--mff-urlbar-results-color) !important;
}

.urlbarView-row[type="bookmark"] > span{
  color: green !important;
}

.urlbarView-row[type="switchtab"] > span{
  color: orange !important;
}

.urlbarView-url, .search-panel-one-offs-container {
  color: var(--mff-urlbar-results-url-color) !important;
  font-family: var(--mff-urlbar-font-family);
  font-weight: var(--mff-urlbar-results-font-weight);
  font-size: var(--mff-urlbar-font-size) !important;
}

.urlbarView-favicon, .urlbarView-type-icon {
  display: none !important;
}

#urlbar-input {
  font-size: var(--mff-urlbar-font-size) !important;
  color: var(--mff-urlbar-color) !important;
  font-family: var(--mff-urlbar-font-family) !important;
  font-weight: var(--mff-urlbar-font-weight)!important;
  text-align: center !important;
}

#tracking-protection-icon-container, #identity-box {
  display: none;
}

#back-button > .toolbarbutton-icon{
  --backbutton-background: transparent !important;
  border: none !important;
}

#back-button {
  list-style-image: url("left-arrow.svg") !important;
}

#forward-button {
  list-style-image: url("right-arrow.svg") !important;
}

toolbar {
  background-image: none !important;
}

#urlbar-background {
  opacity: .98 !important;
}

#navigator-toolbox, toolbaritem {
  border: none !important;
}

#urlbar-background {
  background-color: var(--mff-bg) !important;
  border: none !important;
}

.toolbar-items {
  background-color: var(--mff-bg) !important;
}

#sidebar-search-container {
  background-color: var(--mff-sidebar-bg) !important;
}

box.panel-arrowbox {
  display: none;
}

box.panel-arrowcontent {
  border-radius: 8px !important;
  border: none !important;
}

tab.tabbrowser-tab {
  overflow: hidden;
}

tab.tabbrowser-tab:hover {
  box-shadow: 0 1px 4px rgba(0,0,0,.05);
}

image#star-button {
  display: none;
}

toolbar#nav-bar {
  padding: var(--mff-nav-toolbar-padding) !important;
}

toolbar#nav-bar {
  padding: 4px !important;
}

#urlbar {
  max-width: 70% !important;
  margin: 0 15% !important;
  /* 	position: unset!important; */;
}

#urlbar-input:focus {
  color: var(--mff-urlbar-focused-color) !important;
}


.megabar[breakout-extend="true"]:not([open="true"]) > #urlbar-background {
  box-shadow: none !important;
  background-color: transparent !important;
}

toolbarbutton {
  box-shadow: none !important;
}


/*
  ___ ___ ___  ___ ___   _   ___
 / __|_ _|   \| __| _ ) /_\ | _ \
 \__ \| || |) | _|| _ \/ _ \|   /
 |___/___|___/|___|___/_/ \_\_|_\
*/

.close-icon, .urlbar-icon {
  fill: var(--mff-icon-color) !important;
}

.sidebar-placesTree {
  color: var(--mff-sidebar-color) !important;
}

#sidebar-switcher-target {
/*   color: white !important; */
}

#sidebar-box {
  --sidebar-background-color: var(--mff-sidebar-bg) !important;
}

splitter#sidebar-splitter {
  opacity: 0 !important;
}

splitter#sidebar-splitter {
  border: none !important;
  background-color: transparent !important;
}

image#sidebar-icon {
  display: none;
}


/*
    _   ___ ___  _____      _____  _   _  _ ___ _
   /_\ | _ \ _ \/ _ \ \    / / _ \/_\ | \| | __| |
  / _ \|   /   / (_) \ \/\/ /|  _/ _ \| .` | _|| |__
 /_/ \_\_|_\_|_\\___/ \_/\_/ |_|/_/ \_\_|\_|___|____|
 */

.panel-arrowcontent {
  padding: 0px !important;
  margin: 0px !important;
}

toolbarseparator {
  display: none;
}