diff --git a/browser/base/content/browser.css b/browser/base/content/browser.css
index e360d266851b..5edd24c81f98 100644
--- a/browser/base/content/browser.css
+++ b/browser/base/content/browser.css
@@ -77,12 +77,15 @@ body {
        (-moz-os-version: windows-win8) {
   :root:-moz-lwtheme {
     background-color: var(--lwt-accent-color);
+    background-image: var(--lwt-additional-images);
+    background-repeat: var(--lwt-background-tiling);
+    background-position: var(--lwt-background-alignment);
   }
 
   :root[lwtheme-image] {
-    background-image: var(--lwt-header-image) !important;
-    background-repeat: no-repeat;
-    background-position: right top !important;
+    background-image: var(--lwt-header-image, linear-gradient(transparent, transparent)),  var(--lwt-additional-images) !important;
+    background-repeat: no-repeat, var(--lwt-background-tiling);
+    background-position: right top, var(--lwt-background-alignment) !important;
   }
 
   :root:-moz-lwtheme:-moz-window-inactive {
diff --git a/toolkit/components/extensions/test/browser/browser_ext_themes_additional_backgrounds_alignment.js b/toolkit/components/extensions/test/browser/browser_ext_themes_additional_backgrounds_alignment.js
index 2db6cf84c14b..cc814b4ae80c 100644
--- a/toolkit/components/extensions/test/browser/browser_ext_themes_additional_backgrounds_alignment.js
+++ b/toolkit/components/extensions/test/browser/browser_ext_themes_additional_backgrounds_alignment.js
@@ -33,8 +33,8 @@ add_task(async function test_default_additional_backgrounds_alignment() {
 
     Assert.equal(
       rootCS.getPropertyValue("background-position"),
-      RIGHT_TOP,
-      "root only contains theme_frame alignment property"
+      `${RIGHT_TOP}, ${RIGHT_TOP}`,
+      "root contains theme_frame and lwt-background-alignment properties"
     );
     Assert.equal(
       toolboxCS.getPropertyValue("background-position"),
@@ -98,8 +98,8 @@ add_task(async function test_additional_backgrounds_alignment() {
     let rootCS = window.getComputedStyle(docEl);
     Assert.equal(
       rootCS.getPropertyValue("background-position"),
-      RIGHT_TOP,
-      "root only contains theme_frame alignment property"
+      `${RIGHT_TOP}, ${LEFT_BOTTOM}, ${CENTER_CENTER}, ${RIGHT_TOP}`,
+      "root contains theme_frame and additional_backgrounds alignment properties"
     );
     Assert.equal(
       toolboxCS.getPropertyValue("background-position"),
diff --git a/toolkit/components/extensions/test/browser/browser_ext_themes_multiple_backgrounds.js b/toolkit/components/extensions/test/browser/browser_ext_themes_multiple_backgrounds.js
index 2b5558e8a229..7d837bfc0d4e 100644
--- a/toolkit/components/extensions/test/browser/browser_ext_themes_multiple_backgrounds.js
+++ b/toolkit/components/extensions/test/browser/browser_ext_themes_multiple_backgrounds.js
@@ -156,7 +156,7 @@ add_task(async function test_support_backgrounds_repeat() {
     );
     Assert.equal(
       rootCS.backgroundPosition,
-      "100% 0%",
+      "100% 0%, 100% 0%",
       "The backgroundPosition should use the default value for root."
     );
     Assert.equal(
@@ -166,7 +166,7 @@ add_task(async function test_support_backgrounds_repeat() {
     );
     Assert.equal(
       rootCS.backgroundRepeat,
-      "no-repeat",
+      "no-repeat, repeat-x, repeat-y, repeat",
       "The backgroundRepeat should use the default values for root."
     );
     Assert.equal(
@@ -253,13 +253,13 @@ add_task(async function test_additional_images_check() {
     );
     Assert.equal(
       rootCS.backgroundPosition,
-      "100% 0%",
+      "100% 0%, 100% 0%",
       "The backgroundPosition should use the default value."
     );
     Assert.equal(
       rootCS.backgroundRepeat,
-      "no-repeat",
-      "The backgroundPosition should use only one (default) value."
+      "no-repeat, no-repeat",
+      "The backgroundPosition should use only one (default) value for the header and the default additional images."
     );
   } else {
     let bgImage = toolboxCS.backgroundImage.split(",")[0].trim();