--- a/devtools/server/actors/storage.js
+++ b/devtools/server/actors/storage.js
@@ -1451,17 +1451,17 @@ StorageActors.createActor({
 
   populateStoresForHost: Task.async(function*(host) {
     let storeMap = new Map();
     let {names} = yield this.getDBNamesForHost(host);
 
     for (let name of names) {
       let metadata = yield this.getDBMetaData(host, name);
 
-      indexedDBHelpers.patchMetadataMapsAndProtos(metadata);
+      metadata = indexedDBHelpers.patchMetadataMapsAndProtos(metadata);
       storeMap.set(name, metadata);
     }
 
     this.hostVsStores.set(host, storeMap);
   }),
 
   /**
    * Returns the over-the-wire implementation of the indexed db entity.
@@ -1724,32 +1724,32 @@ var indexedDBHelpers = {
   Task.async(function*(host, name = "null", options, hostVsStores) {
     name = JSON.parse(name);
     if (!name || !name.length) {
       // This means that details about the db in this particular host are
       // requested.
       let dbs = [];
       if (hostVsStores.has(host)) {
         for (let [, db] of hostVsStores.get(host)) {
-          indexedDBHelpers.patchMetadataMapsAndProtos(db);
+          db = indexedDBHelpers.patchMetadataMapsAndProtos(db);
           dbs.push(db.toObject());
         }
       }
       return this.backToChild("getValuesForHost", {dbs: dbs});
     }
 
     let [db2, objectStore, id] = name;
     if (!objectStore) {
       // This means that details about all the object stores in this db are
       // requested.
       let objectStores = [];
       if (hostVsStores.has(host) && hostVsStores.get(host).has(db2)) {
         let db = hostVsStores.get(host).get(db2);
 
-        indexedDBHelpers.patchMetadataMapsAndProtos(db);
+        db = indexedDBHelpers.patchMetadataMapsAndProtos(db);
 
         let objectStores2 = db.objectStores;
 
         for (let objectStore2 of objectStores2) {
           objectStores.push(objectStore2[1].toObject());
         }
       }
       return this.backToChild("getValuesForHost", {objectStores: objectStores});
@@ -1844,31 +1844,46 @@ var indexedDBHelpers = {
     };
     request.onerror = () => {
       db.close();
       success.resolve([]);
     };
     return success.promise;
   },
 
+  /**
+   * When indexedDB metadata is parsed to and from JSON then the object's
+   * prototype is dropped and any Maps are changed to arrays of arrays. This
+   * method is used to repair the prototypes and fix any broken Maps.
+   */
   patchMetadataMapsAndProtos: function(metadata) {
-    for (let [, store] of metadata._objectStores) {
-      store.__proto__ = ObjectStoreMetadata.prototype;
+    let md = Object.create(DatabaseMetadata.prototype);
+    Object.assign(md, metadata);
+
+    md._objectStores = new Map(metadata._objectStores);
+
+    for (let [name, store] of md._objectStores) {
+      let obj = Object.create(ObjectStoreMetadata.prototype);
+      Object.assign(obj, store);
+
+      md._objectStores.set(name, obj);
 
       if (typeof store._indexes.length !== "undefined") {
-        store._indexes = new Map(store._indexes);
+        obj._indexes = new Map(store._indexes);
       }
 
-      for (let [, value] of store._indexes) {
-        value.__proto__ = IndexMetadata.prototype;
+      for (let [name2, value] of obj._indexes) {
+        let obj2 = Object.create(IndexMetadata.prototype);
+        Object.assign(obj2, value);
+
+        obj._indexes.set(name2, obj2);
       }
     }
 
-    metadata._objectStores = new Map(metadata._objectStores);
-    metadata.__proto__ = DatabaseMetadata.prototype;
+    return md;
   },
 
   handleChildRequest: function(msg) {
     let host;
     let name;
     let args = msg.data.args;
 
     switch (msg.json.method) {