--- a/browser/base/content/browser-addons.js
+++ b/browser/base/content/browser-addons.js
@@ -803,17 +803,17 @@ var LightweightThemeListener = {
 
   uninit() {
     Services.obs.removeObserver(this, "lightweight-theme-styling-update");
     Services.obs.removeObserver(this, "lightweight-theme-optimized");
   },
 
   /**
    * Set the headerImage to a CSS variable which is used to apply the background-image
-   * property of all rulesets in browser-lightweightTheme.css.
+   * property of the respective rulesets in tabs.inc.css.
    *
    * @param headerImage - a string containing a CSS image for the lightweight theme header.
    */
   updateStyleSheet(headerImage) {
     document.documentElement.style.setProperty("--lwt-header-image", headerImage);
 },
   // nsIObserver
   observe(aSubject, aTopic, aData) {

--- a/browser/base/content/browser.xul
+++ b/browser/base/content/browser.xul
@@ -8,17 +8,16 @@
 
 <?xml-stylesheet href="chrome://browser/content/browser.css" type="text/css"?>
 <?xml-stylesheet href="chrome://browser/content/places/places.css" type="text/css"?>
 <?xml-stylesheet href="chrome://browser/content/usercontext/usercontext.css" type="text/css"?>
 <?xml-stylesheet href="chrome://devtools/skin/devtools-browser.css" type="text/css"?>
 <?xml-stylesheet href="chrome://browser/skin/controlcenter/panel.css" type="text/css"?>
 <?xml-stylesheet href="chrome://browser/skin/customizableui/panelUI.css" type="text/css"?>
 <?xml-stylesheet href="chrome://browser/skin/" type="text/css"?>
-<?xml-stylesheet href="chrome://browser/skin/browser-lightweightTheme.css" type="text/css"?>
 
 <?xul-overlay href="chrome://global/content/editMenuOverlay.xul"?>
 <?xul-overlay href="chrome://browser/content/baseMenuOverlay.xul"?>
 <?xul-overlay href="chrome://browser/content/places/placesOverlay.xul"?>
 
 # All DTD information is stored in a separate file so that it can be shared by
 # hiddenWindow.xul.
 #include browser-doctype.inc

deleted file mode 100644
--- a/browser/themes/linux/browser-lightweightTheme.css
+++ /dev/null
@@ -1,31 +0,0 @@
-/* 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 http://mozilla.org/MPL/2.0/. */
-
-%include linuxShared.inc
-%filter substitution
-
-/*
- * LightweightThemeListener will set the current lightweight theme's header
- * image to the lwt-header-image variable, used in each of the following rulesets.
- */
-
-/* Lightweight theme on tabs */
-#tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab > .tab-stack > .tab-background > .tab-background-start[selected=true]:-moz-lwtheme::before,
-#tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab > .tab-stack > .tab-background > .tab-background-end[selected=true]:-moz-lwtheme::before {
-  background-attachment: scroll, fixed;
-  background-color: transparent;
-  background-image: @fgTabTextureLWT@, var(--lwt-header-image);
-  background-position: 0 0, right top;
-  background-repeat: repeat-x, no-repeat;
-}
-
-#tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab > .tab-stack > .tab-background > .tab-background-middle[selected=true]:-moz-lwtheme {
-  background-attachment: scroll, scroll, fixed;
-  background-color: transparent;
-  background-image: url(chrome://browser/skin/tabbrowser/tab-active-middle.png),
-                    @fgTabTextureLWT@,
-                    var(--lwt-header-image);
-  background-position: 0 0, 0 0, right top;
-  background-repeat: repeat-x, repeat-x, no-repeat;
-}

--- a/browser/themes/linux/jar.mn
+++ b/browser/themes/linux/jar.mn
@@ -7,17 +7,16 @@ browser.jar:
 % override chrome://global/skin/icons/warning-16.png moz-icon://stock/gtk-dialog-warning?size=menu
 #include ../shared/jar.inc.mn
   skin/classic/browser/sanitizeDialog.css
   skin/classic/browser/aboutSessionRestore-window-icon.png
   skin/classic/browser/aboutSyncTabs.css
 * skin/classic/browser/syncedtabs/sidebar.css     (syncedtabs/sidebar.css)
 * skin/classic/browser/browser.css
 * skin/classic/browser/compacttheme.css
-* skin/classic/browser/browser-lightweightTheme.css
   skin/classic/browser/click-to-play-warning-stripes.png
   skin/classic/browser/Info.png
   skin/classic/browser/menuPanel-customize.png
   skin/classic/browser/menuPanel-customize@2x.png
   skin/classic/browser/menuPanel-exit.png
   skin/classic/browser/menuPanel-exit@2x.png
   skin/classic/browser/menuPanel-help.png
   skin/classic/browser/menuPanel-help@2x.png

deleted file mode 100644
--- a/browser/themes/osx/browser-lightweightTheme.css
+++ /dev/null
@@ -1,38 +0,0 @@
-/* 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 http://mozilla.org/MPL/2.0/. */
-
-%include shared.inc
-
-/*
- * LightweightThemeListener will set the current lightweight theme's header
- * image to the lwt-header-image variable, used in each of the following rulesets.
- */
-
-/* Lightweight theme on tabs */
-#tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab > .tab-stack > .tab-background > .tab-background-start[selected=true]:-moz-lwtheme::before,
-#tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab > .tab-stack > .tab-background > .tab-background-end[selected=true]:-moz-lwtheme::before {
-  background-attachment: scroll, fixed;
-  background-color: transparent;
-  background-image: @fgTabTextureLWT@, var(--lwt-header-image);
-  background-position: 0 0, right top;
-  background-repeat: repeat-x, no-repeat;
-}
-
-#tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab > .tab-stack > .tab-background > .tab-background-middle[selected=true]:-moz-lwtheme {
-  background-attachment: scroll, scroll, fixed;
-  background-color: transparent;
-  background-image: url(chrome://browser/skin/tabbrowser/tab-active-middle.png),
-                    @fgTabTextureLWT@,
-                    var(--lwt-header-image);
-  background-position: 0 0, 0 0, right top;
-  background-repeat: repeat-x, repeat-x, no-repeat;
-}
-
-@media (min-resolution: 2dppx) {
-  #tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab > .tab-stack > .tab-background > .tab-background-middle[selected=true]:-moz-lwtheme {
-    background-image: url(chrome://browser/skin/tabbrowser/tab-active-middle@2x.png),
-                      @fgTabTextureLWT@,
-                      var(--lwt-header-image);
-  }
-}

--- a/browser/themes/osx/jar.mn
+++ b/browser/themes/osx/jar.mn
@@ -6,17 +6,16 @@ browser.jar:
 % skin browser classic/1.0 %skin/classic/browser/
 #include ../shared/jar.inc.mn
   skin/classic/browser/sanitizeDialog.css
   skin/classic/browser/aboutSessionRestore-window-icon.png
   skin/classic/browser/aboutSyncTabs.css
 * skin/classic/browser/syncedtabs/sidebar.css          (syncedtabs/sidebar.css)
 * skin/classic/browser/browser.css
 * skin/classic/browser/compacttheme.css
-* skin/classic/browser/browser-lightweightTheme.css
   skin/classic/browser/click-to-play-warning-stripes.png
   skin/classic/browser/Info.png
   skin/classic/browser/keyhole-circle.png
   skin/classic/browser/keyhole-circle@2x.png
   skin/classic/browser/subtle-pattern.png
   skin/classic/browser/menu-back.png
   skin/classic/browser/menu-forward.png
   skin/classic/browser/menuPanel-customize.png

--- a/browser/themes/shared/tabs.inc.css
+++ b/browser/themes/shared/tabs.inc.css
@@ -378,38 +378,64 @@
   background-repeat: repeat-x;
   background-size: var(--tab-stroke-background-size), auto 100%;
   /* The padding-top combined with background-clip: content-box (the bottom-most) ensure the
      background-color doesn't extend above the top border. */
   padding-top: 2px;
 }
 
 /* Selected tab lightweight theme styles.
-   See browser-lightweightTheme.css for information about run-time changes to LWT styles. */
+   See the "Lightweight theme on tabs" section of this file
+   for information about run-time changes to LWT styles. */
 .tab-background-middle[selected=true]:-moz-lwtheme {
   background-color: transparent;
   background-image: url(chrome://browser/skin/tabbrowser/tab-active-middle.png),
-                    @fgTabTextureLWT@;/*,
-                    lwtHeader;*/
+                    @fgTabTextureLWT@;
   /* Don't stretch the LWT header images */
   background-size: var(--tab-stroke-background-size), auto 100%, auto auto;
 }
 
-/* These LWT styles are normally overridden by browser-lightweightTheme.css */
+/* These LWT styles are normally overridden by the "Lightweight theme on tabs"
+   section of this file. */
 .tab-background-start[selected=true]:-moz-lwtheme::before,
 .tab-background-end[selected=true]:-moz-lwtheme::before {
   background-image: @fgTabTextureLWT@;
 }
 
 .tab-background-start[selected=true]:-moz-lwtheme::before,
 .tab-background-end[selected=true]:-moz-lwtheme::before,
 .tab-background-middle[selected=true]:-moz-lwtheme {
   background-color: transparent;
 }
 
+/*
+ * LightweightThemeListener will set the current lightweight theme's header
+ * image to the lwt-header-image variable, used in each of the following rulesets.
+ */
+
+/* Lightweight theme on tabs */
+#tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab > .tab-stack > .tab-background > .tab-background-start[selected=true]:-moz-lwtheme::before,
+#tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab > .tab-stack > .tab-background > .tab-background-end[selected=true]:-moz-lwtheme::before {
+  background-attachment: scroll, fixed;
+  background-color: transparent;
+  background-image: @fgTabTextureLWT@, var(--lwt-header-image);
+  background-position: 0 0, right top;
+  background-repeat: repeat-x, no-repeat;
+}
+
+#tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab > .tab-stack > .tab-background > .tab-background-middle[selected=true]:-moz-lwtheme {
+  background-attachment: scroll, scroll, fixed;
+  background-color: transparent;
+  background-image: url(chrome://browser/skin/tabbrowser/tab-active-middle.png),
+                    @fgTabTextureLWT@,
+                    var(--lwt-header-image);
+  background-position: 0 0, 0 0, right top;
+  background-repeat: repeat-x, repeat-x, no-repeat;
+}
+
 /* End selected tab */
 
 /* new tab button border and gradient on hover */
 .tabbrowser-tab:hover > .tab-stack > .tab-background:not([selected=true]),
 .tabs-newtab-button:hover {
   background-image: url(chrome://browser/skin/tabbrowser/tab-background-start.png),
                     url(chrome://browser/skin/tabbrowser/tab-background-middle.png),
                     url(chrome://browser/skin/tabbrowser/tab-background-end.png);
@@ -525,16 +551,22 @@
     background-image: url(chrome://browser/skin/tabbrowser/tab-stroke-start@2x.png);
   }
 
   .tab-background-end[selected=true]:-moz-locale-dir(ltr)::after,
   .tab-background-start[selected=true]:-moz-locale-dir(rtl)::after {
     background-image: url(chrome://browser/skin/tabbrowser/tab-stroke-end@2x.png);
   }
 
+  #tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab > .tab-stack > .tab-background > .tab-background-middle[selected=true]:-moz-lwtheme {
+    background-image: url(chrome://browser/skin/tabbrowser/tab-active-middle@2x.png),
+                      @fgTabTextureLWT@,
+                      var(--lwt-header-image);
+  }
+
   .tab-throbber[busy] {
     list-style-image: url("chrome://browser/skin/tabbrowser/connecting@2x.png");
   }
 
   .tab-icon-image {
     list-style-image: url("chrome://mozapps/skin/places/defaultFavicon@2x.png");
   }
 

deleted file mode 100644
--- a/browser/themes/windows/browser-lightweightTheme.css
+++ /dev/null
@@ -1,39 +0,0 @@
-/* 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 http://mozilla.org/MPL/2.0/. */
-
-%include windowsShared.inc
-%filter substitution
-
-/*
- * LightweightThemeListener will set the current lightweight theme's header
- * image to the lwt-header-image variable, used in each of the following rulesets.
- */
-
-/* Lightweight theme on tabs */
-#tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab > .tab-stack > .tab-background > .tab-background-start[selected=true]:-moz-lwtheme::before,
-#tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab > .tab-stack > .tab-background > .tab-background-end[selected=true]:-moz-lwtheme::before {
-  background-attachment: scroll, fixed;
-  background-color: transparent;
-  background-image: @fgTabTextureLWT@, var(--lwt-header-image);
-  background-position: 0 0, right top;
-  background-repeat: repeat-x, no-repeat;
-}
-
-#tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab > .tab-stack > .tab-background > .tab-background-middle[selected=true]:-moz-lwtheme {
-  background-attachment: scroll, scroll, fixed;
-  background-color: transparent;
-  background-image: url(chrome://browser/skin/tabbrowser/tab-active-middle.png),
-                    @fgTabTextureLWT@,
-                    var(--lwt-header-image);
-  background-position: 0 0, 0 0, right top;
-  background-repeat: repeat-x, repeat-x, no-repeat;
-}
-
-@media (min-resolution: 1.25dppx) {
-  #tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab > .tab-stack > .tab-background > .tab-background-middle[selected=true]:-moz-lwtheme {
-    background-image: url(chrome://browser/skin/tabbrowser/tab-active-middle@2x.png),
-                      @fgTabTextureLWT@,
-                      var(--lwt-header-image);
-  }
-}

--- a/browser/themes/windows/jar.mn
+++ b/browser/themes/windows/jar.mn
@@ -6,17 +6,16 @@ browser.jar:
 % skin browser classic/1.0 %skin/classic/browser/
 #include ../shared/jar.inc.mn
   skin/classic/browser/sanitizeDialog.css
   skin/classic/browser/aboutSessionRestore-window-icon.png
   skin/classic/browser/aboutSyncTabs.css
 * skin/classic/browser/syncedtabs/sidebar.css     (syncedtabs/sidebar.css)
 * skin/classic/browser/browser.css
 * skin/classic/browser/compacttheme.css
-* skin/classic/browser/browser-lightweightTheme.css
   skin/classic/browser/caption-buttons.svg
   skin/classic/browser/click-to-play-warning-stripes.png
   skin/classic/browser/Info.png
   skin/classic/browser/livemark-folder.png
   skin/classic/browser/menu-back.png
   skin/classic/browser/menu-forward.png
   skin/classic/browser/menuPanel-customize.png
   skin/classic/browser/menuPanel-customize@2x.png