This theme is deprecated and will not receive more updates, please use: https://github.com/Guerra24/Firefox-UWP-Style

userChrome.css

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

.titlebar-button, #minimize-button, #restore-button, #close-button {
	width: 46px !important;
	height: 32px !important;
}
#titlebar-buttonbox, #TabsToolbar, #toolbar-menubar {
	height: 32px !important;
}
#toolbar-menubar > #menubar-items > #main-menubar > menu {
	padding: 0px !important;
}
#titlebar {
	margin-top: 1px !important;
	height: 33px !important;
	margin-bottom: -33px !important;
}
window #titlebar-content {
	margin-top: 0px !important;
	height: 32px !important;
}
window[sizemode="maximized"] #titlebar {
	margin-top: 0px !important;
	height: 41px !important;
}
window[sizemode="maximized"] #titlebar-content {
	margin-top: 0px !important;
	height: 32px !important;
}
#titlebar-min, #minimize-button {
	padding-top: 9px !important;
}
window[sizemode="fullscreen"] #minimize-button {
	padding-top: 8px !important;
}
#titlebar-min:hover, #titlebar-max:hover, #minimize-button:hover, #restore-button:hover {
	background-color: var(--titlebar-min-max-hover-bg-color) !important;
}
#titlebar-min:hover:active, #titlebar-max:hover:active, #minimize-button:hover:active, #restore-button:hover:active {
	background-color: var(--titlebar-min-max-active-bg-color) !important;
}
#titlebar-close:hover, #close-button:hover {
	background-color: var(--titlebar-close-hover-bg-color)	!important;
}
#titlebar-close:hover:active, #close-button:hover:active {
	background-color: var(--titlebar-close-active-bg-color) !important;
}
#navigator-toolbox {
	background: black !important;
}
#nav-bar {
	margin-top: 0px !important;
	border-top: 0px !important;
	box-shadow: none !important;
}
#main-window[chromemargin] {
	background-color: rgba(0, 0, 0, 1) !important;
	-moz-appearance: -moz-win-glass !important;
}
#nav-bar textbox {
	background-color: rgba(42, 42, 42, 0) !important;
}
#nav-bar textbox:hover {
	background-color: rgba(75, 75, 75, 1) !important;
}
#urlbar, .searchbar-textbox {
	border: 0px !important;
	height: 20px !important;
}
#urlbar {
	margin-left: 1px !important;
	margin-right: 1px !important;
}
#nav-bar[id], #PersonalToolbar[id], #web-developer-toolbar[id], #navigator-toolbox[tabsontop="true"] > #nav-bar[id], #navigator-toolbox[tabsontop="true"]:not([customizing]) > #nav-bar[collapsed="true"][id] + toolbar, #navigator-toolbox[tabsontop="true"]:not([customizing]) > #nav-bar[collapsed="true"] + #customToolbars + #PersonalToolbar[id], #navigator-toolbox[tabsontop="false"] > #nav-bar[id], #navigator-toolbox[tabsontop="false"]:not([customizing]) > #nav-bar[collapsed="true"][id] + toolbar, #navigator-toolbox[tabsontop="false"]:not([customizing]) > #nav-bar[collapsed="true"] + #customToolbars + #PersonalToolbar[id] {
	background-image: none !important;
	background: rgba(42, 42, 42, 1) !important;
}
.tabbrowser-tab[selected="true"][pinned="true"]:hover, .tabbrowser-tab:not([pinned]):hover, .tabs-newtab-button:hover, #new-tab-button:hover, #alltabs-button:hover {
	color: rgba(240, 240, 240, 1) !important;
	background: rgba(42, 42, 42, 1) !important;
	border-top: 0px !important;
}
.tab-background-middle[selected="true"], .tabbrowser-tab[selected="true"], .tab-background-middle[selected="true"]:hover, .tabbrowser-tab[selected="true"]:hover {
	background: rgba(42, 42, 42, 1) !important;
}
.tabbrowser-tab[pinned]:hover {
	color: rgba(240, 240, 240, 1) !important;
	background: rgba(42, 42, 42, 1) !important;
	border-top: 0px !important;
}
.tab-background {
	border-top: none !important;
}
.tabbrowser-tab::before, .tabbrowser-tab::after {
	display: none !important;
}
.tabs-newtab-button, #new-tab-button, #alltabs-button {
	color: rgba(240, 240, 240, 1) !important;
	background: rgba(0, 0, 0, 0.0) !important;
	border-top: 0px !important;
	margin-bottom: 0px !important;
}
.tabs-newtab-button:hover:active, #new-tab-button:hover:active, #alltabs-button:hover:active {
	background: #444 !important
}
window:not([chromehidden~="toolbar"]) #urlbar-container > .toolbarbutton-1:-moz-any([disabled], :not([open]):not([disabled]):not(:active)) > .toolbarbutton-icon[class], #main-window:not([customizing]) #back-button[disabled] > .toolbarbutton-icon[class] {
	background-image: none !important;
	background-color: rgba(40, 40, 40, 0) !important;
	box-shadow: none !important;
	border: 0px !important;
}
#forward-button, #back-button {
	display: none !important;
}
toolbarbutton.bookmark-item {
	border: 1px rgba(0, 0, 0, 0) solid !important;
}
toolbarbutton.bookmark-item:hover {
	background-color: rgba(75, 75, 75, 1) !important;
	border: 1px rgba(75, 75, 75, 1) solid !important;
}
.titlebar-placeholder[type="pre-tabs"] {
	display: none !important;
}
.titlebar-placeholder[type="post-tabs"] {
	width: 50px !important;
}
#content-deck {
	-moz-appearance: -moz-win-exclude-glass !important;
}
#TabsToolbar {
	background: black !important;
	margin-bottom: 0px !important;
}
#navigator-toolbox::after {
	border-bottom: 0px !important;
}
browser[type="content-primary"], browser[type="content"] {
	background: #303030 !important;
}
browser, browser.display.background_color, tabbrowser tabpanels {
	background-color: #303030 !important;
}
#TabsToolbar .tab-background {
	background: transparent !important;
	border-right: 0px !important;
	border-left: 0px !important;
}
.scrollbutton-up, .scrollbutton-down {
	margin-bottom: 0px !important;
}
.scrollbutton-up:hover, .scrollbutton-down:hover {
	background: rgba(42, 42, 42, 1) !important;
}
.scrollbutton-up:hover:active, .scrollbutton-down:hover:active {
	background: #444 !important;
}
.tabs-newtab-button .toolbarbutton-icon {
	background: transparent !important;
}
#urlbar, .searchbar-textbox {
	box-shadow: none !important;
}
.close-icon > .toolbarbutton-icon {
	border-radius: 0px !important;
}
#TabsToolbar[movingtab] {
	padding-bottom: 0px !important;
}
#TabsToolbar[movingtab] > .tabbrowser-tabs {
	padding-bottom: 0px !important;
	margin-bottom: 0px !important;
}
#new-tab-button > .toolbarbutton-icon, #alltabs-button > .toolbarbutton-icon {
	background-color: transparent !important;
}
:root {
	--titlebar-min-max-hover-bg-color: rgba(42, 42, 42, 1);
	--titlebar-min-max-active-bg-color: #444;
	--titlebar-close-hover-bg-color: #E81123;
	--titlebar-close-active-bg-color: #F06F79;
	--toolbarbutton-border-radius: 0px !important;
	--tab-min-height: 32px !important;
}
menupopup {
	-moz-appearance: none !important;
	padding: 8px 2px 8px 2px !important;
	background-color: #2B2B2B !important;
	border: 1px #A0A0A0 solid !important;
	min-width: 280px !important;
}
menuseparator {
	-moz-appearance: none !important;
	border: none !important;
	padding: .5px 0px .5px 0px !important;
	margin: 4px 8px 4px 8px !important;
	background-color: #808080 !important;
}
menuitem, menu {
	-moz-appearance: none !important;
	color: white !important;
	padding: 7.5px 0px 7.5px 0px !important;
}
menuitem[disabled="true"], menuitem[disabled="true"] > .menu-text {
	color: gray !important;
}
menuitem:hover, menu:hover, menu[open="true"], menuitem[_moz-menuactive="true"]	 {
	-moz-appearance: none !important;
	padding: 7.5px 0px 7.5px 0px !important;
	background-color: #414141 !important;
}
menugroup {
	padding: 0px !important;
	background-color: transparent !important;
}
menuitem > .menu-text, menuitem > .menu-iconic-text {
	color: white !important;
}
menuitem[type="checkbox"] {
	padding-left: 8px !important;
	padding-top: 6.5px !important;
	padding-bottom: 6.5px !important;
}
menuitem[type="radio"] {
	padding-left: 8px !important;
	padding-top: 6.5px !important;
	padding-bottom: 6.5px !important;
}
menuitem[type="checkbox"] > .menu-iconic-text, menuitem[type="radio"] > .menu-iconic-text {
	padding-left: 5px !important;
}
menuitem[checked="true"][type="checkbox"] > .menu-iconic-left {
	padding: 7px 0px 0px 0px !important;
	border: solid white;
	border-width: 0 0 2px 2px;
	transform: rotate(-45deg) scale(.75);
	margin-bottom: 4px !important;
}
menuitem[checked="true"][type="radio"] > .menu-iconic-left {
	padding: 1px !important;
	border: solid white;
	height: 17px !important;
	border-radius: 100%;
	background: white;
	transform: scale(.5); 
}
menucaption {
	background-color: transparent !important;
	color: white !important;
}
#ContentSelectDropdown > menupopup {
	background-image: none !important;
}
#ContentSelectDropdown {
	padding: 0px !important;
}
menulist {
	-moz-appearance: none !important;
	padding: 4px 4px 4px 4px !important;
	border: 2px solid #666666 !important;
	background-color: transparent !important;
}
menulist:hover {
	padding: 4px 4px 4px 4px !important;
	border: 2px solid #999999 !important;
	background-color: transparent !important;
}
menulist[open="true"]  {
	border: 2px solid #666666 !important;
	background-color: #333333 !important;
}
#context-back > .menu-iconic-left, #context-forward > .menu-iconic-left, #context-reload > .menu-iconic-left, #context-stop > .menu-iconic-left, #context-bookmarkpage > .menu-iconic-left {
	padding: 0px !important;
}
.menu-iconic-left {
	-moz-appearance: none !important;
	padding: 0px 5px 0px 9px !important;
}
.menu-right {
	-moz-appearance: none !important;
	padding: 7.5px !important;
	margin-right: 6px !important;
	color: white !important;
	border: solid white;
	border-width: 0 2px 2px 0px;
	transform: rotate(-45deg) scale(.55);
}
tooltip {
	-moz-appearance: none !important;
	color: white !important;
	background-color: #2B2B2B !important;
	border: 1px solid #767676 !important;
	padding: 6.5px !important;
}
#tabbrowser-tabs {
	--tab-line-color: -moz-win-accentcolor !important;
	--tab-loading-fill: -moz-win-accentcolor !important;
}
#tabbrowser-tabs:-moz-window-inactive {
	--tab-line-color: rgb(128, 128, 128) !important;
}

userContent.css

/*AGENT_SHEET*/

@-moz-document url(about:newtab), url(about:home) {
	body{
		background-color: #303030 !important;
		color: #D1D1D1 !important;
		overflow: hidden !important;
    }
	#newtab-customize-overlay {
		background: #323234 !important;
	}
	.card, .prefs-pane .sidebar {
		background-color: #2c2c2c !important; /*202020*/
		color: #C4C4C4 !important;
	}
	.prefs-pane .actions {
		background-color: #2c2c2c !important;
		border-left: 1px solid #D7D7DB;
	}
	.prefs-pane .prefs-modal-inner-wrapper .options {
		background-color: #2c2c2c !important; /*202020*/
		color: #C4C4C4 !important;
	}
	.prefs-pane-button button {
		border: 1px solid #525A6D !important;
		fill: #EEE !important;
	}
	.prefs-pane-button button:hover {
		background-color: #444444 !important;
		border: 1px solid #525A6D !important;
	}
	.prefs-pane-button button:active {
		background-color: #323234 !important;
		border: 1px solid #525A6D !important;
	}
	.search-wrapper input {
		background: #474749 !important;
		color: #FFF !important;
	}
	.contentSearchHeader, .contentSearchSuggestionTable, .contentSearchSettingButton, .contentSearchHeaderRow {
		background: #2c2c2c !important;
		color: #FFF !important;
		-moz-appearance: none !important;
		border-color: transparent !important;
	}
	.search-wrapper .search-label, .search-wrapper .search-button {
		fill: #EEE !important; 
	}
	.search-wrapper .search-button:focus, .search-wrapper .search-button:hover {
		background-color: #444444 !important;
	}
	.search-wrapper .search-button:active {
		background-color: #323234 !important;
	}
	.section-top-bar .info-option {
		background: #2c2c2c !important;
		color: #FFF !important;
		-moz-appearance: none !important;
		border-color: transparent !important;
	}
	.context-menu {
		background: #2c2c2c !important;
		color: #C4C4C4 !important;
		-moz-appearance: none !important;
		border-color: transparent !important;
	}
	.separator {
		border: 1px solid #525A6D !important;
	}
	.icon {
		fill: #C4C4C4 !important;
	}
	.onboarding-watermark {
		display: none !important;
	}
}