--- a/browser/base/content/browser-addons.js
+++ b/browser/base/content/browser-addons.js
@@ -637,44 +637,35 @@ var LightWeightThemeWebInstaller = {
       }
     }
 
     if (this._isAllowed(baseURI)) {
       this._install(data, notify);
       return;
     }
 
-    let allowButtonText =
-      gNavigatorBundle.getString("lwthemeInstallRequest.allowButton");
-    let allowButtonAccesskey =
-      gNavigatorBundle.getString("lwthemeInstallRequest.allowButton.accesskey");
-    let message =
-      gNavigatorBundle.getFormattedString("lwthemeInstallRequest.message",
-                                          [uri.host]);
-    let buttons = [{
-      label: allowButtonText,
-      accessKey: allowButtonAccesskey,
-      callback() {
+    let strings = {
+      header: gNavigatorBundle.getFormattedString("webextPerms.header", [data.name]),
+      text: gNavigatorBundle.getFormattedString("lwthemeInstallRequest.message2",
+                                                [uri.host]),
+      acceptText: gNavigatorBundle.getString("lwthemeInstallRequest.allowButton2"),
+      acceptKey: gNavigatorBundle.getString("lwthemeInstallRequest.allowButton.accesskey2"),
+      cancelText: gNavigatorBundle.getString("webextPerms.cancel.label"),
+      cancelKey: gNavigatorBundle.getString("webextPerms.cancel.accessKey"),
+      msgs: []
+    };
+    ExtensionsUI.showPermissionsPrompt(gBrowser.selectedBrowser, strings, null,
+      "installWeb").then(answer => {
+      if (answer) {
         LightWeightThemeWebInstaller._install(data, notify);
       }
-    }];
-
-    this._removePreviousNotifications();
-
-    let notificationBox = gBrowser.getNotificationBox();
-    let notificationBar =
-      notificationBox.appendNotification(message, "lwtheme-install-request", "",
-                                         notificationBox.PRIORITY_INFO_MEDIUM,
-                                         buttons);
-    notificationBar.persistence = 1;
+    });
   },
 
   _install(newLWTheme, notify) {
-    let previousLWTheme = this._manager.currentTheme;
-
     let listener = {
       onEnabling(aAddon, aRequiresRestart) {
         if (!aRequiresRestart) {
           return;
         }
 
         let messageString = gNavigatorBundle.getFormattedString("lwthemeNeedsRestart.message",
           [aAddon.name], 1);
@@ -693,69 +684,26 @@ var LightWeightThemeWebInstaller = {
 
         PopupNotifications.show(gBrowser.selectedBrowser, "addon-theme-change",
                                 messageString, "addons-notification-icon",
                                 action, null, options);
       },
 
       onEnabled(aAddon) {
         if (notify) {
-          LightWeightThemeWebInstaller._postInstallNotification(newLWTheme, previousLWTheme);
+          ExtensionsUI.showInstallNotification(gBrowser.selectedBrowser, newLWTheme);
         }
       }
     };
 
     AddonManager.addAddonListener(listener);
     this._manager.currentTheme = newLWTheme;
     AddonManager.removeAddonListener(listener);
   },
 
-  _postInstallNotification(newTheme, previousTheme) {
-    function text(id) {
-      return gNavigatorBundle.getString("lwthemePostInstallNotification." + id);
-    }
-
-    let buttons = [{
-      label: text("undoButton"),
-      accessKey: text("undoButton.accesskey"),
-      callback() {
-        LightWeightThemeWebInstaller._manager.forgetUsedTheme(newTheme.id);
-        LightWeightThemeWebInstaller._manager.currentTheme = previousTheme;
-      }
-    }, {
-      label: text("manageButton"),
-      accessKey: text("manageButton.accesskey"),
-      callback() {
-        BrowserOpenAddonsMgr("addons://list/theme");
-      }
-    }];
-
-    this._removePreviousNotifications();
-
-    let notificationBox = gBrowser.getNotificationBox();
-    let notificationBar =
-      notificationBox.appendNotification(text("message"),
-                                         "lwtheme-install-notification", "",
-                                         notificationBox.PRIORITY_INFO_MEDIUM,
-                                         buttons);
-    notificationBar.persistence = 1;
-    notificationBar.timeout = Date.now() + 20000; // 20 seconds
-  },
-
-  _removePreviousNotifications() {
-    let box = gBrowser.getNotificationBox();
-
-    ["lwtheme-install-request",
-     "lwtheme-install-notification"].forEach(function(value) {
-        let notification = box.getNotificationWithValue(value);
-        if (notification)
-          box.removeNotification(notification);
-      });
-  },
-
   _preview(dataString, baseURI) {
     if (!this._isAllowed(baseURI))
       return;
 
     let data = this._manager.parseTheme(dataString, baseURI);
     if (!data)
       return;
 

--- a/browser/locales/en-US/chrome/browser/browser.properties
+++ b/browser/locales/en-US/chrome/browser/browser.properties
@@ -217,27 +217,21 @@ unsignedAddonsDisabled.learnMore.accessk
 # LOCALIZATION NOTE (compactLightTheme.name): This is displayed in about:addons -> Appearance
 compactLightTheme.name=Compact Light
 compactLightTheme.description=A compact theme with a light color scheme.
 
 # LOCALIZATION NOTE (compactDarkTheme.name): This is displayed in about:addons -> Appearance
 compactDarkTheme.name=Compact Dark
 compactDarkTheme.description=A compact theme with a dark color scheme.
 
-# LOCALIZATION NOTE (lwthemeInstallRequest.message): %S will be replaced with
+# LOCALIZATION NOTE (lwthemeInstallRequest.message2): %S will be replaced with
 # the host name of the site.
-lwthemeInstallRequest.message=This site (%S) attempted to install a theme.
-lwthemeInstallRequest.allowButton=Allow
-lwthemeInstallRequest.allowButton.accesskey=a
-
-lwthemePostInstallNotification.message=A new theme has been installed.
-lwthemePostInstallNotification.undoButton=Undo
-lwthemePostInstallNotification.undoButton.accesskey=U
-lwthemePostInstallNotification.manageButton=Manage Themes…
-lwthemePostInstallNotification.manageButton.accesskey=M
+lwthemeInstallRequest.message2=This site (%S) attempted to install a theme.
+lwthemeInstallRequest.allowButton2=Allow
+lwthemeInstallRequest.allowButton.accesskey2=a
 
 # LOCALIZATION NOTE (lwthemeNeedsRestart.message):
 # %S will be replaced with the new theme name.
 lwthemeNeedsRestart.message=%S will be installed after you restart.
 lwthemeNeedsRestart.button=Restart Now
 lwthemeNeedsRestart.accesskey=R
 
 # LOCALIZATION NOTE (popupWarning.message): Semicolon-separated list of plural forms.