diff --git a/packages/taler-wallet-webextension/src/wallet/DeveloperPage.tsx b/packages/taler-wallet-webextension/src/wallet/DeveloperPage.tsx
index cbf6b1c0a..0916f4f43 100644
--- a/packages/taler-wallet-webextension/src/wallet/DeveloperPage.tsx
+++ b/packages/taler-wallet-webextension/src/wallet/DeveloperPage.tsx
@@ -197,6 +197,30 @@ export function View({
             <i18n.Translate>run gc</i18n.Translate>
           </Button>
         </Grid>
+        <Grid item>
+          <Button
+            variant="contained"
+            onClick={() => {
+              return api.background.call("sum", [1, 2, 3]).then((r) => {
+                console.log("SUM", r);
+              });
+            }}
+          >
+            <i18n.Translate>sum 123</i18n.Translate>
+          </Button>
+        </Grid>
+        <Grid item>
+          <Button
+            variant="contained"
+            onClick={() => {
+              return api.background.call("freeze", 5000).then(() => {
+                console.log("WAIT");
+              });
+            }}
+          >
+            <i18n.Translate>freeze 5000</i18n.Translate>
+          </Button>
+        </Grid>
         <Grid item>
           <Button
             variant="contained"
diff --git a/packages/taler-wallet-webextension/src/wxApi.ts b/packages/taler-wallet-webextension/src/wxApi.ts
index ea087fc5d..4ec51fc78 100644
--- a/packages/taler-wallet-webextension/src/wxApi.ts
+++ b/packages/taler-wallet-webextension/src/wxApi.ts
@@ -53,6 +53,14 @@ export interface ExtendedPermissionsResponse {
 }
 
 export interface BackgroundOperations {
+  freeze: {
+    request: number;
+    response: void;
+  };
+  sum: {
+    request: number[],
+    response: number,
+  }
   resetDb: {
     request: void;
     response: void;
diff --git a/packages/taler-wallet-webextension/src/wxBackend.ts b/packages/taler-wallet-webextension/src/wxBackend.ts
index c94b390ff..d54dc818f 100644
--- a/packages/taler-wallet-webextension/src/wxBackend.ts
+++ b/packages/taler-wallet-webextension/src/wxBackend.ts
@@ -162,7 +162,19 @@ async function toggleHeaderListener(
   return { newValue: false };
 }
 
+function freeze(time: number): Promise<void> {
+  return new Promise((res, rej) => {
+    setTimeout(res, time)
+  })
+}
+
+async function sum(ns: Array<number>): Promise<number> {
+  return ns.reduce((prev, cur) => prev + cur, 0)
+}
+
 const backendHandlers: BackendHandlerType = {
+  freeze,
+  sum,
   containsHeaderListener,
   getDiagnostics,
   resetDb,