userChrome.css

/* Removes the hover effect from most buttons */
toolbar {
  --toolbarbutton-hover-background: initial !important;
}

/*
  NAV BAR (TABS)
*/

/* reduces the tab bar height */
:root,
#tabbrowser-tabs {
  --tab-min-height: 20px !important;
}
.tab-background {
  margin-block: 0 !important;
}
#TabsToolbar-customization-target,
#tabbrowser-arrowscrollbox,
#tabbrowser-tabs {
  height: var(--tab-min-height);
}
/* hides the tab bar when in 'new window' mode */
window[chromehidden^="menubar"] #titlebar {
  height: 0;
}
/* hides the firefox icon on the top-left */
#firefox-view-button {
  display: none;
}
/* removes the vertical bar next to the firefox icon */
#tabbrowser-tabs {
  padding-inline-start: 0 !important;
  border-inline-start: none !important;
  margin-inline-start: 0 !important;
}
.tabbrowser-tab {
  padding: 0 !important;
}
/* removes left-hand spacing on Windows */
.titlebar-spacer {
  display: none;
}
/* remove rounded corners on tabs */
.tab-background {
  border-radius: 0 !important;
}

/* hides the 'X' (close) button from tab until hover */
.tab-close-button {
  visibility: collapse;
}
.tabbrowser-tab:hover .tab-close-button {
  visibility: visible;
}

/* disables the close button hover effect */ 
.close-icon:hover {
  background-color: initial !important;
}
/* hides the audio playing / secondary label from tabs */
.tab-secondary-label {
  display: none !important;
}

/* hide the '+' (new tab) button from the tab bar until hover */
#tabs-newtab-button {
  visibility: hidden;
}
#TabsToolbar:hover #tabs-newtab-button {
  visibility: visible;
}

/* prepend the tab number before tab name */
.browser-toolbar {
  counter-reset: tabindex;
}
.tab-label::before {
  counter-increment: tabindex;
  content: counter(tabindex) ". ";
  white-space: pre;
  opacity: 0.6;
}

/* remove window control when in fullscreen (minimize/fullscreen/close) */
#window-controls toolbarbutton {
  display: none;
}

/* hides the All tabs button */
#alltabs-button {
  display: none !important;
}

/*
   URL BAR
*/

/* reduces the urlbar height */
#urlbar {
  --urlbar-toolbar-height: 25px !important;
}
#urlbar-container {
  --urlbar-container-height: 25px !important;
}
#nav-bar-customization-target > toolbarbutton > image,
toolbarbutton stack {
  padding: calc(var(--toolbarbutton-inner-padding) / 2) !important;
  padding-top: 0 !important;
  padding-bottom: 0 !important;
  height: initial !important;
  width: initial !important;
}
#nav-bar {
  height: 25px !important;
}

/* reduces the searchbar/navbar height */
#urlbar,
.searchbar-textbox {
  min-height: initial !important;
  margin: 0 !important;
}

/* pushes the urlbar inline with other items */
.urlbar-input-box {
  display: inline-flex;
}

#titlebar {
  appearance: initial !important;
}
/* normalize icon sizes and spaces between them */
.toolbar-items toolbarbutton {
  padding: 0 0 !important;
}
toolbarbutton {
  padding-top: 0 !important;
  padding-bottom: 0 !important;
}

/* uses the "bookmark this page" (star) icon for the bookmark menu */
#bookmarks-menu-button {
  list-style-image: url("chrome://browser/skin/bookmark-hollow.svg") !important;
}
/* removes the extensions button */
#unified-extensions-button, #unified-extensions-button image {
  width: 1px !important;
  padding: 0 !important;
  list-style-image: none !important;
}

/* hides the harmburger icon separator */
#PanelUI-button {
  border: none !important;
}

/* removes extra spacing around hamburger icon */
#PanelUI-button,
#PanelUI-menu-button {
  padding-inline-start: 0 !important;
  padding-inline-end: 0 !important;
}

/*
	URLBAR TEXTBOX
*/

/* hides the placeholder text in search bar */
#urlbar-input::placeholder {
  color: transparent;
}

/* makes the textbox the same color as the rest of the navbar */
#urlbar-background {
  background-color: var(--toolbar-bgcolor) !important;
}

/* hides the 'go' icon */ 
#urlbar-go-button {
  display: none !important;
}

/*
	URLBAR TEXTBOX - LEFT
*/

/* Hides the magnifying glass icon when no page is loaded */ 
#identity-box[pageproxystate="invalid"] #identity-icon {
  list-style-image: none !important;
}


/* hides the tracking protection (shield) icon until we hover on the urlbar */
#tracking-protection-icon-box {
  visibility: hidden !important;
}
#nav-bar:hover #tracking-protection-icon-box {
  visibility: initial !important;
}

/* Hides the lock icon until we hover on the urlbar */ 
#identity-box[pageproxystate="valid"].verifiedDomain #identity-icon,
#identity-box[pageproxystate="valid"].mixedActiveBlocked #identity-icon {
  width: 1px !important;
}
#nav-bar:hover #identity-box[pageproxystate="valid"].verifiedDomain #identity-icon,
#nav-bar:hover #identity-box[pageproxystate="valid"].mixedActiveBlocked #identity-icon {
  width: initial !important;
}

/* Hides the permission icon until we hover on the urlbar */ 
#permissions-granted-icon {
  width: 1px !important;
}
#nav-bar:hover #permissions-granted-icon {
  width: initial !important;
}

/* Hides the password icon until we hover on the urlbar */ 
#password-notification-icon {
  width: 1px !important;
}
#nav-bar:hover #password-notification-icon {
  width: initial !important;
}

/* Fixes height of the password icon */ 
#notification-popup-box {
  height: 16px !important;
}

/* Disables hover effect (background color change) */
#notification-popup-box:hover,
#identity-icon-box:hover,
#tracking-protection-icon-container:hover {
  background-color: initial !important;
}

/* fixes spacing caused by hiding certificates */
#identity-box {
  padding-inline-end: 4px !important;
  margin-inline-end: 4px !important;
}

/* removes the right-hand border next to certificates text */
#identity-box {
  border: none !important;
}

/* Pushes identity, permissions and certificates to the right of the navbar */ 
#remote-control-box {
  order: 5;
}
#tracking-protection-icon-container {
  order: 6;
}
#identity-box {
  order: 7;
}

/*
	URLBAR TEXTBOX - RIGHT
*/

/* removes the reader icon and seperator */
#pageActionSeparator,
#reader-mode-button {
  visibility: collapse !important;
}

/* removes the history button */
.urlbar-history-dropmarker {
  display: none;
}

/* removes the bookmark button */
#star-button-box {
  display: none !important;
}

/* removes the page action button */
#pageActionButton {
  display: none !important;
}

/*
  URLBAR SUGGESTIONS POPUP 
*/

/* remove search engines from suggestions popup */ 
.search-one-offs {
  display: none !important;
}

/* reduces suggestion height */
.urlbarView-row {
  min-height: initial !important;
}
.urlbarView-row-inner {
  min-height: initial !important;
  padding: 3px !important;
}

/*
	BOOKMARKS MENU
*/

/* Remove "Show All Bookmarks" (top) menu item */
#BMB_bookmarksShowAllTop,
/* remove "Display bookmarks sidebar" menu item */
#BMB_viewBookmarksSidebar,
/* remove "Bookmarks Toolbar" menu item */
#BMB_bookmarksToolbar,
/* Hides all separators */
#BMB_bookmarksPopup menuseparator {
  display: none;
}

/* Adjust "Show All Bookmarks" and "Open all in tabs" size */
#BMB_bookmarksShowAll,
.openintabs-menuitem {
  min-height: initial !important;
}

/* Reduces spacing between bookmark menu items  */
menupopup > menu, menupopup > menuitem { 
  padding-block: 2px !important;
}

/*
 DOWNLOADS MENU
*/
/* reduces height of most items */
.downloadTypeIcon {
  width: 16px !important;
  height: 16px !important;
}
.downloadButton {
  height: 16px !important;
  min-width: 16px !important;
}
.downloadDetails {
  margin-top: 0 !important;
  margin-bottom: 0 !important;
}
.downloadMainArea {
  padding-block: 0 !important;
}
#downloadsListBox > richlistitem {
  min-height: 0 !important;
  margin: 0 0 2px !important;
}
#downloadsHistory {
  padding: 0 !important;
}
/*
	HISTORY MENU
*/

/* Remove "View History Sidebar" menu item */
#appMenuViewHistorySidebar,
/* Remove "Clear Recent History" menu item */
#appMenuClearRecentHistory,
/* Remove "Recently Closed Tabs" menu item */
#appMenuRecentlyClosedTabs,
/* Remove "Recently Closed Windows" menu item */
#appMenuRecentlyClosedWindows,
/* Remove "Recent History" label */
#PanelUI-history .subview-subheader {
  display: none;
}

/* Hides all separators */
#PanelUI-history toolbarseparator {
  visibility: collapse;
}

/* Adjust "Show All History" size */
#PanelUI-historyMore {
  min-height: initial !important;
}

/*
	HAMBURGER ICON
*/

/* Remove "Sign in to Sync" menu item */
#appMenu-fxa-status2,
/* Remove "Content Blocking" menu item */
#appMenu-mainView toolbaritem[closemenu],
/* Remove "Zoom" menu item */
#appMenu-zoom-controls,
/* Remove "Edit" menu item */
#appMenu-edit-controls,
/* Remove "Library" menu item */
#appMenu-library-button,
/* Remove "Add-Ons" menu item */
#appMenu-addons-button,
/* Remove "Find in this page" menu item */
#appMenu-find-button2,
/* Remove "Help" menu item */
#appMenu-help-button2,
/* Remove "Quit" menu item */
#appMenu-quit-button2,
/* Remove "Add-ons and themes" menu item */
#appMenu-extensions-themes-button,
/* Hides all separators */
#appMenu-mainView toolbarseparator {
  display: none !important;
}

/*
	ADD/EDIT BOOKMARK
*/

/* Remove preview image, favicon */
#editBookmarkPanelFaviconContainer,
#editBookmarkPanelImage {
  display: none !important;
}

/* Hides "Show editor when saving" toggle button */
#editBookmarkPanelBottomContent {
  display: none !important;
}

/* Hides "Tags" textbox */
.editBMPanel_tagsRow {
  display: none !important;
}

/* Show "Keyword" textbox */
.editBMPanel_keywordRow {
  display: initial !important;
}