--- a/browser/themes/linux/compacttheme.css
+++ b/browser/themes/linux/compacttheme.css
@@ -3,29 +3,29 @@
 % file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 %include ../shared/compacttheme.inc.css
 
 :root {
   --forwardbutton-width: 29px;
 }
 
-:root[devtoolstheme="light"] {
+:root:-moz-lwtheme-darktext {
   --urlbar-dropmarker-url: url("chrome://browser/skin/devedition/urlbar-history-dropmarker.svg");
   --urlbar-dropmarker-region: rect(0px, 11px, 14px, 0px);
   --urlbar-dropmarker-hover-region: rect(0, 22px, 14px, 11px);
   --urlbar-dropmarker-active-region: rect(0px, 33px, 14px, 22px);
   --urlbar-dropmarker-2x-url: url("chrome://browser/skin/devedition/urlbar-history-dropmarker.svg");
   --urlbar-dropmarker-2x-region: rect(0px, 11px, 14px, 0px);
   --urlbar-dropmarker-hover-2x-region: rect(0, 22px, 14px, 11px);
   --urlbar-dropmarker-active-2x-region: rect(0px, 33px, 14px, 22px);
 }
 
-:root[devtoolstheme="dark"] .findbar-closebutton:not(:hover),
-:root[devtoolstheme="dark"] #sidebar-header > .close-icon:not(:hover),
+:root:-moz-lwtheme-brighttext .findbar-closebutton:not(:hover),
+:root:-moz-lwtheme-brighttext #sidebar-header > .close-icon:not(:hover),
 .tab-close-button[selected]:not(:hover) {
   background-image: -moz-image-rect(url("chrome://global/skin/icons/close.svg"), 0, 80, 16, 64);
 }
 
 /* The menubar and tabs toolbar should match the devedition theme */
 #TabsToolbar,
 #toolbar-menubar {
   -moz-appearance: none !important;

--- a/browser/themes/osx/compacttheme.css
+++ b/browser/themes/osx/compacttheme.css
@@ -101,24 +101,24 @@
   padding-bottom: 3px !important;
 }
 
 #PanelUI-button {
   margin-top: 0;
   margin-bottom: 0;
 }
 
-:root[devtoolstheme="dark"] .findbar-closebutton:not(:hover),
+:root:-moz-lwtheme-brighttext .findbar-closebutton:not(:hover),
 /* Tab styling - make sure to use an inverted icon for the selected tab
    (brighttext only covers the unselected tabs) */
 .tab-close-button[selected=true]:not(:hover) {
   -moz-image-region: rect(0, 64px, 16px, 48px);
 }
 @media (min-resolution: 2dppx) {
-  :root[devtoolstheme="dark"] .findbar-closebutton:not(:hover),
+  :root:-moz-lwtheme-brighttext .findbar-closebutton:not(:hover),
   .tab-close-button[selected=true]:not(:hover) {
     -moz-image-region: rect(0, 128px, 32px, 96px);
   }
 }
 
 .ac-type-icon {
   /* Left-align the type icon in awesomebar popup results with the icon in the
      urlbar. */

--- a/browser/themes/shared/compacttheme.inc.css
+++ b/browser/themes/shared/compacttheme.inc.css
@@ -9,17 +9,17 @@
 :root {
   --tab-toolbar-navbar-overlap: 0px;
   --navbar-tab-toolbar-highlight-overlap: 0px;
   --space-above-tabbar: 0px;
   --toolbarbutton-text-shadow: none;
   --backbutton-urlbar-overlap: 0px;
 }
 
-:root[devtoolstheme="dark"] {
+:root:-moz-lwtheme-brighttext {
   /* Chrome */
   --chrome-background-color: #272b35;
   --chrome-color: #F5F7FA;
   --chrome-secondary-background-color: #393F4C;
   --chrome-navigator-toolbox-separator-color: rgba(0,0,0,.2);
   --chrome-nav-bar-separator-color: rgba(0,0,0,.2);
   --chrome-nav-buttons-background: #252C33;
   --chrome-nav-buttons-hover-background: #1B2127;
@@ -45,29 +45,29 @@
   --urlbar-dropmarker-active-region: rect(0px, 33px, 14px, 22px);
   --urlbar-dropmarker-2x-url: url("chrome://browser/skin/devedition/urlbar-history-dropmarker.svg");
   --urlbar-dropmarker-2x-region: rect(0px, 11px, 14px, 0px);
   --urlbar-dropmarker-hover-2x-region: rect(0, 22px, 14px, 11px);
   --urlbar-dropmarker-active-2x-region: rect(0px, 33px, 14px, 22px);
 }
 
 /* Override the lwtheme-specific styling for toolbar buttons */
-:root[devtoolstheme="dark"],
-:root[devtoolstheme="dark"] toolbar:-moz-lwtheme {
+:root:-moz-lwtheme-brighttext,
+:root:-moz-lwtheme-brighttext toolbar:-moz-lwtheme {
   --toolbarbutton-hover-background: rgba(25,33, 38,.6) linear-gradient(rgba(25,33,38,.6), rgba(25,33,38,.6)) padding-box;
   --toolbarbutton-hover-boxshadow: none;
   --toolbarbutton-hover-bordercolor: rgba(25,33,38,.6);
   --toolbarbutton-active-background: rgba(25,33,38,1) linear-gradient(rgba(25,33,38,1), rgba(25,33,38,1)) border-box;
   --toolbarbutton-active-boxshadow: none;
   --toolbarbutton-active-bordercolor: rgba(25,33,38,.8);
   --toolbarbutton-checkedhover-backgroundcolor: #3C5283;
 
 }
 
-:root[devtoolstheme="light"] {
+:root:-moz-lwtheme-darktext {
   --url-and-searchbar-background-color: #fff;
 
   --chrome-background-color: #E3E4E6;
   --chrome-color: #18191a;
   --chrome-secondary-background-color: #f5f6f7;
   --chrome-navigator-toolbox-separator-color: #cccccc;
   --chrome-nav-bar-separator-color: #B6B6B8;
   --chrome-nav-buttons-background: #ffffff; /* --theme-body-background */
@@ -80,18 +80,18 @@
   --tab-hover-background-color: #D7D8DA;
   --tab-selection-color: #f5f7fa;
   --tab-selection-background-color: #4c9ed9;
   --tab-selection-box-shadow: none;
   --pinned-tab-glow: radial-gradient(22px at center calc(100% - 2px), rgba(76,158,217,0.9) 13%, transparent 16%);
 }
 
 /* Override the lwtheme-specific styling for toolbar buttons */
-:root[devtoolstheme="light"],
-:root[devtoolstheme="light"] toolbar:-moz-lwtheme {
+:root:-moz-lwtheme-darktext,
+:root:-moz-lwtheme-darktext toolbar:-moz-lwtheme {
   --toolbarbutton-hover-background: #eaeaea;
   --toolbarbutton-hover-boxshadow: none;
   --toolbarbutton-hover-bordercolor: rgba(0,0,0,0.1);
   --toolbarbutton-active-background: #d7d7d8 border-box;
   --toolbarbutton-active-boxshadow: none;
   --toolbarbutton-active-bordercolor: rgba(0,0,0,0.15);
   --toolbarbutton-checkedhover-backgroundcolor: #d7d7d8;
 }
@@ -192,37 +192,37 @@ toolbar[brighttext] #downloads-indicator
   background-color: var(--url-and-searchbar-background-color) !important;
   background-image: none !important;
   color: inherit !important;
   border: 1px solid var(--chrome-nav-bar-controls-border-color) !important;
   box-shadow: none !important;
 }
 
 %filter substitution
-%define selectorPrefix :root[devtoolstheme="dark"] 
+%define selectorPrefix :root:-moz-lwtheme-brighttext 
 %define selectorSuffix :-moz-lwtheme
 %define iconVariant -white
 %include identity-block/icons.inc.css
 
 #urlbar {
   border-inline-start: none !important;
   opacity: 1 !important;
 }
 
 window:not([chromehidden~="toolbar"]) #urlbar-wrapper {
   overflow: -moz-hidden-unscrollable;
   clip-path: none;
   margin-inline-start: 0;
 }
 
-:root[devtoolstheme="dark"] #urlbar-zoom-button:hover {
+:root:-moz-lwtheme-brighttext #urlbar-zoom-button:hover {
   background-color: rgba(255,255,255,.2);
 }
 
-:root[devtoolstheme="dark"] #urlbar-zoom-button:hover:active {
+:root:-moz-lwtheme-brighttext #urlbar-zoom-button:hover:active {
   background-color: rgba(255,255,255,.3);
 }
 
 /* Nav bar specific stuff */
 #nav-bar {
   margin-top: 0 !important;
   border-top: none !important;
   border-bottom: none !important;

--- a/browser/themes/windows/compacttheme.css
+++ b/browser/themes/windows/compacttheme.css
@@ -3,18 +3,18 @@
 % file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 %include ../shared/compacttheme.inc.css
 
 :root {
   --forwardbutton-width: 29px;
 }
 
-:root[devtoolstheme="dark"],
-:root[devtoolstheme="light"] {
+:root:-moz-lwtheme-brighttext,
+:root:-moz-lwtheme-darktext {
    /* Matches the #browser-border-start, #browser-border-end color */
   --chrome-nav-bar-separator-color: rgba(10, 31, 51, 0.35);
 }
 
 /* The window background is white due to no accentcolor in the lightweight
    theme. It can't be changed to transparent when there is no compositor
    (Win 7 in classic / basic theme), or else dragging and focus become
    broken. So instead just show the normal titlebar in that case, and override
@@ -95,27 +95,27 @@
 .tabbrowser-tab {
   background-color: var(--tab-background-color);
 }
 
 #toolbar-menubar {
   text-shadow: none !important;
 }
 
-:root[devtoolstheme="dark"] .findbar-closebutton,
-:root[devtoolstheme="dark"] #sidebar-header > .close-icon,
+:root:-moz-lwtheme-brighttext .findbar-closebutton,
+:root:-moz-lwtheme-brighttext #sidebar-header > .close-icon,
 /* Tab styling - make sure to use an inverted icon for the selected tab
    (brighttext only covers the unselected tabs) */
 .tab-close-button[selected=true] {
   list-style-image: url("chrome://global/skin/icons/close-inverted.png");
 }
 
 @media (min-resolution: 1.1dppx) {
-  :root[devtoolstheme="dark"] .findbar-closebutton,
-  :root[devtoolstheme="dark"] #sidebar-header > .close-icon,
+  :root:-moz-lwtheme-brighttext .findbar-closebutton,
+  :root:-moz-lwtheme-brighttext #sidebar-header > .close-icon,
   .tab-close-button[selected=true] {
     list-style-image: url("chrome://global/skin/icons/close-inverted@2x.png");
   }
 }
 
 @media (-moz-os-version: windows-win7),
        (-moz-os-version: windows-win8) {
   :root {
@@ -274,44 +274,44 @@
 @media (-moz-os-version: windows-win10) {
   /* Always keep draggable space on the sides of tabs since there is no top margin on Win10 */
   #main-window .tabbrowser-arrowscrollbox > .arrowscrollbox-scrollbox {
     padding-left: 15px;
     padding-right: 15px;
   }
 
   /* Force white caption buttons for the dark theme on Windows 10 */
-  :root[devtoolstheme="dark"] #titlebar-min {
+  :root:-moz-lwtheme-brighttext #titlebar-min {
     list-style-image: url(chrome://browser/skin/caption-buttons.svg#minimize-white);
   }
-  :root[devtoolstheme="dark"] #titlebar-max {
+  :root:-moz-lwtheme-brighttext #titlebar-max {
     list-style-image: url(chrome://browser/skin/caption-buttons.svg#maximize-white);
   }
-  #main-window[devtoolstheme="dark"][sizemode="maximized"] #titlebar-max {
+  #main-window:-moz-lwtheme-brighttext[sizemode="maximized"] #titlebar-max {
     list-style-image: url(chrome://browser/skin/caption-buttons.svg#restore-white);
   }
-  :root[devtoolstheme="dark"] #titlebar-close {
+  :root:-moz-lwtheme-brighttext #titlebar-close {
     list-style-image: url(chrome://browser/skin/caption-buttons.svg#close-white);
   }
 
   /* ... and normal ones for the light theme on Windows 10 */
-  :root[devtoolstheme="light"] #titlebar-min {
+  :root:-moz-lwtheme-darktext #titlebar-min {
     list-style-image: url(chrome://browser/skin/caption-buttons.svg#minimize);
   }
-  :root[devtoolstheme="light"] #titlebar-max {
+  :root:-moz-lwtheme-darktext #titlebar-max {
     list-style-image: url(chrome://browser/skin/caption-buttons.svg#maximize);
   }
-  #main-window[devtoolstheme="light"][sizemode="maximized"] #titlebar-max {
+  #main-window:-moz-lwtheme-darktext[sizemode="maximized"] #titlebar-max {
     list-style-image: url(chrome://browser/skin/caption-buttons.svg#restore);
   }
-  :root[devtoolstheme="light"] #titlebar-close {
+  :root:-moz-lwtheme-darktext #titlebar-close {
     list-style-image: url(chrome://browser/skin/caption-buttons.svg#close);
   }
 
-  :root[devtoolstheme="light"] #titlebar-close:hover {
+  :root:-moz-lwtheme-darktext #titlebar-close:hover {
     list-style-image: url(chrome://browser/skin/caption-buttons.svg#close-white);
   }
 }
 
 .ac-type-icon {
   /* Left-align the type icon in awesomebar popup results with the icon in the
      urlbar. */
   margin-inline-start: 13px;