Backed out changeset 4029dc1e969b (bug 1654984) for failures on browser_startup_mainthreadio.js. CLOSED TREE

toolkit/modules/JSONFile.jsm

@@ -268,10 +268,7 @@ JSONFile.prototype = {
         }
       }
 
-      if (
-        this._options.backupTo &&
-        new FileUtils.File(this._options.backupTo).exists()
-      ) {
+      if (this._options.backupTo) {
         // Restore the original file from the backup here so fresh writes to empty
         // json files don't happen at any time in the future compromising the backup
         // in the process.
@@ -372,10 +369,7 @@ JSONFile.prototype = {
         }
       }
 
-      if (
-        this._options.backupTo &&
-        new FileUtils.File(this._options.backupTo).exists()
-      ) {
+      if (this._options.backupTo) {
         // Restore the original file from the backup here so fresh writes to empty
         // json files don't happen at any time in the future compromising the backup
         // in the process.
@@ -389,7 +383,7 @@ JSONFile.prototype = {
 
         try {
           // We still read from the backup file here instead of the original file in case
-          // access to the original file is blocked. For e.g. by anti-virus softwares on
+          // access to the original file is blocked. For eg. by anti-virus softwares on
           // the user's computer.
           // This reads the file and automatically detects the UTF-8 encoding.
           let inputStream = new FileInputStream(