--- a/toolkit/components/passwordmgr/test/unit/head_storage_legacy_1.js
+++ b/toolkit/components/passwordmgr/test/unit/head_storage_legacy_1.js
@@ -138,25 +138,27 @@ const LoginTest = {
    *
    * Counts the number of lines in the specified file.
    */
   countLinesInFile : function (aPathName,  aFileName) {
     var inputFile  = Cc["@mozilla.org/file/local;1"].
                      createInstance(Ci.nsILocalFile);
     inputFile.initWithPath(aPathName);
     inputFile.append(aFileName);
+    if (inputFile.fileSize == 0)
+      return 0;
 
     var inputStream = Cc["@mozilla.org/network/file-input-stream;1"].
                       createInstance(Ci.nsIFileInputStream);
     // init the stream as RD_ONLY, -1 == default permissions.
     inputStream.init(inputFile, 0x01, -1, null);
     var lineStream = inputStream.QueryInterface(Ci.nsILineInputStream);
 
     var line = { value : null };
-    var lineCount = 1;
+    var lineCount = 1; // Empty files were dealt with above.
     while (lineStream.readLine(line)) 
         lineCount++;
 
     return lineCount;
   }
 
 };