Merge pull request #2853 from mozilla/bug

A small fix in proxified-containers

src/js/proxified-containers.js

@@ -65,6 +65,10 @@ proxifiedContainers = {
   async delete(cookieStoreId) {
     // Assumes proxy is a properly formatted object
     const proxifiedContainersStore = await proxifiedContainers.retrieveAll();
+    if(!proxifiedContainersStore) {
+      return null;
+    }
+
     const index = proxifiedContainersStore.findIndex(i => i.cookieStoreId === cookieStoreId);
     if (index !== -1) {
       proxifiedContainersStore.splice(index, 1);