userChrome.css

/* Firefox Compact Mode
 *
 * Copyright (c) 2021 Danny Colin
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

:root {
  /* Tabbar: reduce tab margin */
  --tab-block-margin: 4px 3px !important;
}

/* Tab: Reduce height */
.tabbrowser-tab {
  min-height: 24px !important;
}

/* Tab: Ensure tab height doesn't augment when arrowscrollbox is visible  */ 
#tabbrowser-arrowscrollbox {
  --tab-min-height: 31px !important;
  max-height: var(--tab-min-height);
}

/* Tab: Attention icon */
.tabbrowser-tab:is([image], [pinned]) > .tab-stack > .tab-content[attention]:not([selected="true"]), .tabbrowser-tab > .tab-stack > .tab-content[pinned][titlechanged]:not([selected="true"]) {
  background-position-x: left 2px !important;
  background-position-y: bottom 12.5px !important;
}

/* URLBar: Fix vertical alignment */
#urlbar[breakout=true]:not([open="true"]) {
	--urlbar-height: 20px !important;
	--urlbar-toolbar-height: 24px !important;
}

/* URLBar: Fix URL address vertical aligment when megabar is open */
#urlbar[breakout=true][open="true"] {
	--urlbar-toolbar-height: 30px !important;
}

/* URLBar: Reduce row items padding */
.urlbarView-row-inner {
	padding-inline: var(--urlbarView-item-inline-padding);
	padding-block: 2px !important;
}

/* URLBar: Reduce and realign row bookmark icons */
.urlbarView-type-icon {
	width: 10px !important;
	height: 10px !important;
	margin-bottom: 0 !important;
	margin-inline-start: 10px !important;
}

/* URLBar: Reduce "This time, serach with" padding */
#urlbar .search-one-offs:not([hidden]) {
	padding-block: 4px !important;
}

/* Searchbar: Ensure toolbar height doesn't augment when searchbar is visible */
#urlbar-container, 
#search-container {
	padding-block: 0 !important;
}

/* Searchbar: Make sure the min-height of the input is the same as the popup */
#search-container {
  min-width: 192px !important;
}

/* Toolbar: Reduce spacing */
#urlbar-container {
	--urlbar-container-height: 30px !important;
  margin-top: 0 !important;
}

/* Reload Button: Fix vertical alignment */
#reload-button {
	margin-block-start: -2px !important;
}

/* AppMenu: Header */
.panel-header {
	padding: 4px 0 0 4px !important;
}

/* AppMenu: Header button */
.panel-header > .subviewbutton-back {
	padding: 4px !important;
}

/* Windows 10 context menu */
@media (-moz-os-version: windows-win10) {
  /* Context Menu: Reduce vertical space */
  menupopup > menuitem,
  menupopup > menu {
    padding-block: 2px !important;
  }
}