diff --git a/docs/config.md b/docs/config.md
index 3102eaf83e..a1d6304e2e 100644
--- a/docs/config.md
+++ b/docs/config.md
@@ -32,7 +32,7 @@ For a good example, see https://riot.im/develop/config.json.
    homeserver know what email template to use when talking to you.
 1. `branding`: Configures various branding and logo details, such as:
     1. `welcomeBackgroundUrl`: An image to use as a wallpaper outside the app
-       during authentication flows
+       during authentication flows. If an array is passed, an image is chosen randomly for each visit.
     1. `authHeaderLogoUrl`: An logo image that is shown in the header during
        authentication flows
     1. `authFooterLinks`: a list of links to show in the authentication page footer:
diff --git a/docs/labs.md b/docs/labs.md
index 0605e6c5e2..970a46d1e4 100644
--- a/docs/labs.md
+++ b/docs/labs.md
@@ -67,13 +67,24 @@ An implementation of [MSC2241](https://github.com/matrix-org/matrix-doc/pull/224
 
 This also includes a new implementation of the user & member info panel, designed to share more code between showing community members & room members. Built on top of this new panel is also a new UX for verification from the member panel.
 
-## Cross-signing (in development) (`feature_cross_signing`)
+## Cross-signing
 
 Cross-signing ([MSC1756](https://github.com/matrix-org/matrix-doc/pull/1756))
 improves the device verification experience by allowing you to verify a user
 instead of verifying each of their devices.
 
-This feature is still in development and will be landing in several chunks.
+The feature is enabled by default and does not follow a traditional labs flag
+at the moment. If something goes wrong, add this to your config to disable it:
+```json
+{
+  "settingDefaults": {
+    "feature_cross_signing": false  
+  }
+}
+```
+
+The setting will be removed in a future release, enabling it non-optionally for
+all users.
 
 ## Event indexing and E2EE search support using Seshat (`feature_event_indexing`)
 
diff --git a/src/@types/global.d.ts b/src/@types/global.d.ts
index 6a5adec6d6..a3fb9028c4 100644
--- a/src/@types/global.d.ts
+++ b/src/@types/global.d.ts
@@ -14,25 +14,15 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import "modernizr";
+import "matrix-react-sdk/src/@types/global"; // load matrix-react-sdk's type extensions first
 import {Renderer} from "react-dom";
 
 declare global {
     interface Window {
-        Modernizr: ModernizrAPI & FeatureDetects;
-        Olm: {
-            init: () => Promise<void>;
-        };
-
         mxSendRageshake: (text: string, withLogs?: boolean) => void;
         matrixChat: ReturnType<Renderer>;
 
         // electron-only
         ipcRenderer: any;
     }
-
-    // workaround for https://github.com/microsoft/TypeScript/issues/30933
-    interface ObjectConstructor {
-        fromEntries?(xs: [string|number|symbol, any][]): object
-    }
 }
diff --git a/src/components/views/auth/VectorAuthPage.js b/src/components/views/auth/VectorAuthPage.js
index 98ddb8ba0f..13b43ca1af 100644
--- a/src/components/views/auth/VectorAuthPage.js
+++ b/src/components/views/auth/VectorAuthPage.js
@@ -29,7 +29,11 @@ export default class VectorAuthPage extends React.PureComponent {
         const brandingConfig = SdkConfig.get().branding;
         let backgroundUrl = "themes/riot/img/backgrounds/valley.jpg";
         if (brandingConfig && brandingConfig.welcomeBackgroundUrl) {
-            backgroundUrl = brandingConfig.welcomeBackgroundUrl;
+            if (Array.isArray(brandingConfig.welcomeBackgroundUrl)) {
+                backgroundUrl = brandingConfig.welcomeBackgroundUrl[Math.floor(Math.random() * brandingConfig.welcomeBackgroundUrl.length)];
+            } else {
+                backgroundUrl = brandingConfig.welcomeBackgroundUrl;
+            }
         }
 
         const pageStyle = {