--- a/toolkit/modules/JSONFile.jsm
+++ b/toolkit/modules/JSONFile.jsm
@@ -174,16 +174,20 @@ JSONFile.prototype = {
    * Loads persistent data from the file to memory.
    *
    * @return {Promise}
    * @resolves When the operation finished successfully.
    * @rejects JavaScript exception when dataPostProcessor fails. It never fails
    *          if there is no dataPostProcessor.
    */
   async load() {
+    if (this.dataReady) {
+      return;
+    }
+
     let data = {};
 
     try {
       let bytes = await OS.File.read(this.path, this._options);
 
       // If synchronous loading happened in the meantime, exit now.
       if (this.dataReady) {
         return;