diff --git a/layout/tools/reftest/reftest.js b/layout/tools/reftest/reftest.js
index aa6b5f40db7f..de89a405059c 100644
--- a/layout/tools/reftest/reftest.js
+++ b/layout/tools/reftest/reftest.js
@@ -196,6 +196,10 @@ function StartTests()
         ReadTopManifest(window.arguments[0]);
         BuildUseCounts();
         gTotalTests = gURLs.length;
+
+        if (!gTotalTests)
+            throw "No tests to run";
+
         gURICanvases = {};
         StartCurrentTest();
     } catch (ex) {
@@ -249,7 +253,7 @@ function ReadManifest(aURL)
     var hh = CC[NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX + "http"].
                  getService(CI.nsIHttpProtocolHandler);
     sandbox.http = {};
-    for each (var prop in [ "userAgent", "appName", "appVersion", 
+    for each (var prop in [ "userAgent", "appName", "appVersion",
                             "vendor", "vendorSub", "vendorComment",
                             "product", "productSub", "productComment",
                             "platform", "oscpu", "language", "misc" ])
@@ -488,7 +492,7 @@ function StartCurrentURI(aState)
 {
     gCurrentTestStartTime = Date.now();
     if (gFailureTimeout != null) {
-        dump("REFTEST TEST-UNEXPECTED-FAIL | " + 
+        dump("REFTEST TEST-UNEXPECTED-FAIL | " +
              "| program error managing timeouts\n");
         ++gTestResults.Exception;
     }
@@ -559,13 +563,13 @@ function setupZoom(contentRootElement) {
 function resetZoom() {
     gBrowser.markupDocumentViewer.fullZoom = 1.0;
 }
-    
+
 function OnDocumentLoad(event)
 {
     if (event.target != gBrowser.contentDocument)
         // Ignore load events for subframes.
         return;
-        
+
     if (gClearingForAssertionCheck &&
         gBrowser.contentDocument.location.href == BLANK_URL_FOR_CLEARING) {
         DoAssertionCheck();
@@ -871,7 +875,8 @@ function DocumentLoaded()
             var test_passed = (equal == gURLs[0].equal);
             // what is expected on this platform (PASS, FAIL, or RANDOM)
             var expected = gURLs[0].expected;
-            
+
+            // Not 'const ...' because of 'EXPECTED_*' value dependency.
             var outputs = {};
             const randomMsg = "(EXPECTED RANDOM)";
             outputs[EXPECTED_PASS] = {