--- a/browser/components/extensions/ext-theme.js
+++ b/browser/components/extensions/ext-theme.js
@@ -7,20 +7,24 @@ XPCOMUtils.defineLazyModuleGetter(this, 
 
 // WeakMap[Extension -> Theme]
 let themeMap = new WeakMap();
 
 /** Class representing a theme. */
 class Theme {
   /**
    * Creates a theme instance.
+   *
+   * @param {string} baseURI The base URI of the extension, used to
+   *   resolve relative filepaths.
    */
-  constructor() {
+  constructor(baseURI) {
     // A dictionary of light weight theme styles.
     this.lwtStyles = {};
+    this.baseURI = baseURI;
   }
 
   /**
    * Loads a theme by reading the properties from the extension's manifest.
    * This method will override any currently applied theme.
    *
    * @param {Object} details Theme part of the manifest. Supported
    *   properties can be found in the schema under ThemeType.
@@ -45,37 +49,63 @@ class Theme {
   }
 
   /**
    * Helper method for loading colors found in the extension's manifest.
    *
    * @param {Object} colors Dictionary mapping color properties to values.
    */
   loadColors(colors) {
-    let {accentcolor, textcolor} = colors;
+    for (let color of Object.keys(colors)) {
+      Services.console.logStringMessage(`parsing color=${color}`);
+      let val = colors[color];
+
+      if (!val) {
+        continue;
+      }
 
-    if (accentcolor) {
-      this.lwtStyles.accentcolor = accentcolor;
-    }
+      let cssColor = val;
+      if (Array.isArray(val)) {
+        cssColor = "rgb" + (val.length > 3 ? "a" : "") + "(" + val.join(",") + ")";
+      }
 
-    if (textcolor) {
-      this.lwtStyles.textcolor = textcolor;
+      switch (color) {
+        case "accentcolor":
+        case "frame":
+          this.lwtStyles.accentcolor = cssColor;
+          break;
+        case "textcolor":
+        case "tab_text":
+          this.lwtStyles.textcolor = cssColor;
+          break;
+      }
     }
   }
 
   /**
    * Helper method for loading images found in the extension's manifest.
    *
    * @param {Object} images Dictionary mapping image properties to values.
    */
   loadImages(images) {
-    let {headerURL} = images;
+    for (let image of Object.keys(images)) {
+      let val = images[image];
+
+      if (!val) {
+        continue;
+      }
 
-    if (headerURL) {
-      this.lwtStyles.headerURL = headerURL;
+      switch (image) {
+        case "headerURL":
+        case "theme_frame": {
+          let resolvedURL = this.baseURI.resolve(val);
+          this.lwtStyles.headerURL = resolvedURL;
+          break;
+        }
+      }
     }
   }
 
   /**
    * Unloads the currently applied theme.
    */
   unload() {
     Services.obs.notifyObservers(null,
@@ -86,17 +116,17 @@ class Theme {
 
 /* eslint-disable mozilla/balanced-listeners */
 extensions.on("manifest_theme", (type, directive, extension, manifest) => {
   if (!Preferences.get("extensions.webextensions.themes.enabled")) {
     // Return early if themes are disabled.
     return;
   }
 
-  let theme = new Theme();
+  let theme = new Theme(extension.baseURI);
   theme.load(manifest.theme);
   themeMap.set(extension, theme);
 });
 
 extensions.on("shutdown", (type, extension) => {
   let theme = themeMap.get(extension);
 
   // We won't have a theme if theme's aren't enabled.

--- a/browser/components/extensions/schemas/theme.json
+++ b/browser/components/extensions/schemas/theme.json
@@ -12,27 +12,45 @@
         "properties": {
           "images": {
             "type": "object",
             "optional": true,
             "properties": {
               "headerURL": {
                 "type": "string",
                 "optional": true
+              },
+              "theme_frame": {
+                "type": "string",
+                "optional": true
               }
             }
           },
           "colors": {
             "type": "object",
             "optional": true,
             "properties": {
               "accentcolor": {
                 "type": "string",
                 "optional": true
               },
+              "frame": {
+                "type": "array",
+                "items": {
+                  "type": "number"
+                },
+                "optional": true
+              },
+              "tab_text": {
+                "type": "array",
+                "items": {
+                  "type": "number"
+                },
+                "optional": true
+              },
               "textcolor": {
                 "type": "string",
                 "optional": true
               }
             }
           }
         }
       },

--- a/browser/components/extensions/test/browser/browser-common.ini
+++ b/browser/components/extensions/test/browser/browser-common.ini
@@ -102,16 +102,17 @@ support-files =
 [browser_ext_tabs_query.js]
 [browser_ext_tabs_reload.js]
 [browser_ext_tabs_reload_bypass_cache.js]
 [browser_ext_tabs_sendMessage.js]
 [browser_ext_tabs_cookieStoreId.js]
 [browser_ext_tabs_update.js]
 [browser_ext_tabs_zoom.js]
 [browser_ext_tabs_update_url.js]
+[browser_ext_themes_chromeparity.js]
 [browser_ext_themes_dynamic_updates.js]
 [browser_ext_themes_lwtsupport.js]
 [browser_ext_topwindowid.js]
 [browser_ext_url_overrides.js]
 [browser_ext_webRequest.js]
 [browser_ext_webNavigation_frameId0.js]
 [browser_ext_webNavigation_getFrames.js]
 [browser_ext_webNavigation_urlbar_transitions.js]

new file mode 100644
--- /dev/null
+++ b/browser/components/extensions/test/browser/browser_ext_themes_chromeparity.js
@@ -0,0 +1,55 @@
+"use strict";
+
+const ENCODED_IMAGE_DATA = "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";
+
+function imageBufferFromDataURI(encodedImageData) {
+  let decodedImageData = atob(encodedImageData);
+  return Uint8Array.from(decodedImageData, byte => byte.charCodeAt(0)).buffer;
+}
+
+add_task(function* setup() {
+  yield SpecialPowers.pushPrefEnv({
+    set: [["extensions.webextensions.themes.enabled", true]],
+  });
+});
+
+add_task(function* test_support_theme_frame() {
+  const FRAME_COLOR = [71, 105, 91];
+  const TAB_TEXT_COLOR = [207, 221, 192, .9];
+  let extension = ExtensionTestUtils.loadExtension({
+    manifest: {
+      "theme": {
+        "images": {
+          "theme_frame": "face.png",
+        },
+        "colors": {
+          "frame": FRAME_COLOR,
+          "tab_text": TAB_TEXT_COLOR,
+        },
+      },
+    },
+    files: {
+      "face.png": imageBufferFromDataURI(ENCODED_IMAGE_DATA),
+    },
+  });
+
+  yield extension.startup();
+
+  let docEl = window.document.documentElement;
+
+  Assert.ok(docEl.hasAttribute("lwtheme"), "LWT attribute should be set");
+  Assert.equal(docEl.getAttribute("lwthemetextcolor"), "bright",
+    "LWT text color attribute should be set");
+
+  let style = window.getComputedStyle(docEl);
+  Assert.ok(style.backgroundImage.includes("face.png"),
+    `The backgroundImage should use face.png. Actual value is: ${style.backgroundImage}`);
+  Assert.equal(style.backgroundColor, "rgb(" + FRAME_COLOR.join(", ") + ")",
+    "Expected correct background color");
+  Assert.equal(style.color, "rgba(" + TAB_TEXT_COLOR.join(", ") + ")",
+    "Expected correct text color");
+
+  yield extension.unload();
+
+  Assert.ok(!docEl.hasAttribute("lwtheme"), "LWT attribute should not be set");
+});