--- a/toolkit/components/contextualidentity/ContextualIdentityService.jsm
+++ b/toolkit/components/contextualidentity/ContextualIdentityService.jsm
@@ -216,18 +216,21 @@ function _ContextualIdentityService(path
     try {
       // This reads the file and automatically detects the UTF-8 encoding.
       let inputStream = Cc["@mozilla.org/network/file-input-stream;1"]
                           .createInstance(Ci.nsIFileInputStream);
       inputStream.init(new FileUtils.File(this._path),
                        FileUtils.MODE_RDONLY, FileUtils.PERMS_FILE, 0);
       try {
         let json = Cc["@mozilla.org/dom/json;1"].createInstance(Ci.nsIJSON);
-        this._identities = json.decodeFromStream(inputStream,
-                                                 inputStream.available());
+        let data = json.decodeFromStream(inputStream,
+                                         inputStream.available());
+        this._identities = data.identities;
+        this._lastUserContextId = data.lastUserContextId;
+
         this._dataReady = true;
       } finally {
         inputStream.close();
       }
     } catch (error) {
       this.loadError(error);
       return;
     }