userChrome.css

/*** BEGIN: Override URL bar enlargement ***/
  :root { --mbarstyler-top-bar-display: none; }
  :root #urlbar { --urlbar-toolbar-height: 32.00px !important; }

  /* Compute new position, width, and padding */
  #urlbar[breakout][breakout-extend] {
    top: 5px !important;
    left: 0px !important;
    width: 100% !important;
    padding: 0px !important;}

  /* for alternate UI density settings */
  [uidensity="compact"] #urlbar[breakout][breakout-extend] {
    top: 3px !important;}

  [uidensity="touch"] #urlbar[breakout][breakout-extend] {
    top: 4px !important;}

  /* Prevent shift of URL bar contents */
  #urlbar[breakout][breakout-extend] > #urlbar-input-container {
    height: var(--urlbar-height) !important;
    padding: 0 !important;}

  /* Do not animate */
  #urlbar[breakout][breakout-extend] > #urlbar-background {
    animation: none !important;;}

  /* Remove shadows */
  #urlbar[breakout][breakout-extend] > #urlbar-background {
    box-shadow: none !important;}

  /* Top "Blue Bar" Display */
  .urlbarView-row:first-of-type {
    display: none !important;}

  /* Subtle border between results */
  .urlbarView-row:not(:last-of-type) {
    border-bottom: 1px solid rgba(0, 0, 0, 0.1) !important;}
/*** END: Override URL bar enlargement ***/

/*** BEGIN: Theme toolbar buttons ***/
  :root {--toolbarbutton-outer-padding: 2px !important;}

  .toolbarbutton-1:not(:hover) {
    border: 1px solid #A7A7A7 !important;
    border-radius: 5px !important;
    margin: 0px !important;
    transform: scale(.84,.82) !important;
    background-image: linear-gradient(to top,#E4E4E4,#DADADA);}

  .toolbarbutton-1:hover {
    border: 1px solid #A7A7A7 !important;
    border-radius: 5px !important;
    margin: 0px !important;
    transform: scale(.84,.82) !important;
    background-image: linear-gradient(to top,#E4E4E4,#DADADA);}
/*** END: Theme toolbar buttons ***/

/* Very dirty fix for nav bar edge margins */
#back-button {margin-left: 5px !important;}
#tab-list-single_codefisher_org-browser-action {margin-right: 5px !important;}

/* Remove 'new tab' button */
#new-tab-button,
#tabs-newtab-button {display: none !important;}

#tabs-newtab-button:hover > .toolbarbutton-icon
{display: none !important;}

/* Remove blue animation on tab on page load complete */
.tab-loading-burst {display: none !important;}

/* Remove 'three dots' button in urlbar */
#pageActionSeparator,
#pageActionButton {display: none !important;}

/* Remove menu popover */
#PanelUI-menu-button {display: none !important;}

/* Remove line on top of tabs */
.tab-line {display: none !important;}

/* Set custom 'new tab' favicon (icon must be in chrome folder) */
.tabbrowser-tab[label^="New Tab"] .tab-icon-image {
    list-style-image: none !important;
    width: 0 !important;
    padding-left: 16px !important;
    background: url("default_favicon.png") !important;
    background-size: 16px 16px !important;
    background-repeat: no-repeat !important;}

/* Fix forward/back/etc. contextual menu items */
#context-navigation {-moz-box-orient: vertical !important;}
#context-navigation > menuitem > .menu-iconic-left {display: none !important;}
#context-navigation > menuitem {
  padding-inline-start: 20px !important;
  -moz-box-pack: start !important;}
#context-navigation > menuitem::before {content: attr(aria-label) !important;}

/* Hide contextual menu items */
#context_pinTab, #context_closeTabsToTheEnd,
#context_closeOtherTabs, #context_selectAllTabs,
#context-searchselect {display: none !important;}

#context_closeTabOptions > label,
#context_closeTabOptions > hbox {
  display: none !important;}

/* Increase top and bottom nav bar margins */
#nav-bar {
   padding-top: 5px !important;
   padding-bottom: 5px !important;}

/* Add gradient to nav bar */
.browser-toolbar:not(.titlebar-color) {
  background: #E9E9E9 !important;
  background-image: linear-gradient(to top,#D3D3D3,#EDEDED) !important;}

/* Show tab close button on hover */
.tabbrowser-tab:not(:hover) .tab-close-button {display: none !important;}
.tabbrowser-tab:not([pinned]):hover .tab-close-button {display: block !important;}

/* Make tab close buttons smaller */
.tabbrowser-tab:hover .tab-close-button {
 width: 15px !important;
 height: 15px !important;}

/* Move favicons and close buttons closer to the edges of tabs */
.tab-icon-image[selected="true"] {margin-left: -4px !important;}
.tab-icon-image:not([selected="true"]) {margin-left: -5px !important;}
.tab-close-button {margin-right: -5px !important;}

/* Hide tab overflow scroll buttons */
#scrollbutton-up {display: none !important;}
#scrollbutton-down {display: none !important;}

/* Remove 'show all tabs' button */
#tabbrowser-tabs ~ #alltabs-button {display: none !important;}

/* Hide screenshot and favicon in bookmark editor */
#editBookmarkPanelImage,
#editBookmarkPanelFaviconContainer {display: none !important;}
#editBookmarkPanelRows {padding-top: 2px !important;}

/* Turn tab text black and bold */
#TabsToolbar .tabbrowser-tab:not([selected="true"]) {color: black !important;}
#TabsToolbar .tabbrowser-tab[selected="true"] {color: #3C3C3C !important;}

#TabsToolbar .tabbrowser-tab .tab-content:not([selected="true"]) {
  font-weight: 800 !important;
  text-shadow: 1px 1px #BBBBBB !important;}

#TabsToolbar .tabbrowser-tab .tab-content[selected="true"] {
  font-weight: 800 !important;
  text-shadow: 1px 1px #E2E2E2 !important;}

/*** BEGIN: Restore CTR tabs ***/
  /* Selected tab: Outer (dark) border */
  .tabbrowser-tab[selected="true"] {
    border-left: 1px solid var(--tabs-border-color) !important;
    border-right: 1px solid var(--tabs-border-color) !important;
    border-bottom: 1px solid #9D9E9F !important;
    border-bottom-left-radius: 4px !important;
    border-bottom-right-radius: 4px !important;}

  /* Selected tab: Inner (light) border */
  .tab-background[selected="true"] {
    background-image: linear-gradient(to top,#CECECE,#D3D3D3) !important;
    border-top: 1px solid #D3D3D3 !important;
    border-left: 1px solid #D9D9D9 !important;
    border-right: 1px solid #D9D9D9 !important;
    border-bottom: 1px solid #D9D9D9 !important;
    border-bottom-left-radius: 4px !important;
    border-bottom-right-radius: 4px !important;
    margin-right: -1px !important;}

  /* Unselected tabs: Outer (dark) border */
  .tabbrowser-tab:not([selected="true"]):not(:hover) {
    border-top: 1px solid #7D8185 !important;
    border-left: 1px solid var(--tabs-border-color) !important;
    border-right: 1px solid var(--tabs-border-color) !important;
    border-bottom: 1px solid #88898A !important;
    border-bottom-left-radius: 4px !important;
    border-bottom-right-radius: 4px !important;}

  /* Unselected tabs: Inner (light) border */
  .tab-content:not([selected="true"]):not(:hover) {
    background-image: linear-gradient(to top,#A5A5A5,#959595);
    border-left: 1px solid #A8A8A8 !important;
    border-right: 1px solid #A8A8A8 !important;
    border-bottom: 1px solid #BBBBBB !important;
    border-bottom-left-radius: 4px !important;
    border-bottom-right-radius: 4px !important;
    margin-right: -1px !important;}

  /* Hover unselected tabs: Outer (dark) border */
  .tabbrowser-tab:not([selected="true"]):hover {
    border-top: 1px solid #7D8185 !important;
    border-left: 1px solid var(--tabs-border-color) !important;
    border-right: 1px solid var(--tabs-border-color) !important;
    border-bottom: 1px solid #88898A !important;
    border-bottom-left-radius: 4px !important;
    border-bottom-right-radius: 4px !important;}

  /* Hover unselected tabs: Inner (light) border */
  .tab-content:not([selected="true"]):hover {
    background-image: linear-gradient(to top,#B6B6B6,#ADADAD);
    border-left: 1px solid #A8A8A8 !important;
    border-right: 1px solid #A8A8A8 !important;
    border-bottom: 1px solid #BBBBBB !important;
    border-bottom-left-radius: 4px !important;
    border-bottom-right-radius: 4px !important;
    margin-right: -1px !important;}

  /* Hide default tab separators and borders */
  .tabbrowser-tab::after, .tabbrowser-tab::before {
    opacity: 0 !important;
    border-image: unset !important;
    border-image-slice: unset !important;
    width: unset !important;}

  /* Change background 'underneath' the tabs */
  #TabsToolbar-customization-target {
    background-color: #A1A1A1 !important;
    border-bottom: 1px solid var(--tabs-border-color) !important;}

  /* Remove excess line on bottom of tab bar */
  #navigator-toolbox {border-bottom: unset !important;}
/*** END: Restore CTR tabs ***/

/*** BEGIN: Tab on bottom ***/
  #navigator-toolbox toolbar:not(#nav-bar):not(#toolbar-menubar) {
    -moz-box-ordinal-group:10}
  #TabsToolbar {-moz-box-ordinal-group:1000 !important;}

  #TabsToolbar {
    position: absolute !important;
    bottom: 0 !important;
    width: 100vw !important;
    display: block !important;}

  #tabbrowser-tabs {
    top: 300 !important;
    width: 100vw !important;}

  #main-window:not([chromehidden*="toolbar"]) #navigator-toolbox {
    padding-bottom: calc(1px + var(--tab-min-height_tnot)) !important;}

  /* Tab height */
  :root {
    --tab-toolbar-navbar-overlap: 0px !important;
    --tab-min-height: 28px !important; /* adjust to suit your needs */
    --tab-min-height_tnot: 28px;}

  :root #tabbrowser-tabs {
    --tab-min-height: 28px !important; /* needs to be the same as above */
    --tab-min-width: 90px !important;}

  #TabsToolbar {
    height: var(--tab-min-height) !important;
    margin-bottom: 1px !important;}
/*** END: Tabs on bottom ***/