--- a/dom/tests/mochitest/general/test_img_mutations.html
+++ b/dom/tests/mochitest/general/test_img_mutations.html
@@ -11,21 +11,21 @@
     "use strict";
 
     // Tests the relevant mutations part of the spec for img src and srcset
     // and that img.src still behaves by the older spec. (Bug 1076583)
     // https://html.spec.whatwg.org/#relevant-mutations
     SimpleTest.waitForExplicitFinish();
 
     // 50x50 png
-    var testPNG50 = new URL("image_50.png", location).href;
+    var testPNG50 = new URL("image_50.png?noCache=" + Math.random(), location).href;
     // 100x100 png
-    var testPNG100 = new URL("image_100.png", location).href;
+    var testPNG100 = new URL("image_100.png?noCache=" + Math.random(), location).href;
     // 200x200 png
-    var testPNG200 = new URL("image_200.png", location).href;
+    var testPNG200 = new URL("image_200.png?noCache=" + Math.random(), location).href;
 
     var tests = [];
     var img;
     var expectingErrors = 0;
     var expectingLoads = 0;
     var afterExpectCallback;
 
     function onImgLoad() {