diff --git a/dom/canvas/test/webgl-conformance/conformance/textures/texture-npot-video.html b/dom/canvas/test/webgl-conformance/conformance/textures/texture-npot-video.html
index f50777598c5e..e5e0ad47a9e6 100644
--- a/dom/canvas/test/webgl-conformance/conformance/textures/texture-npot-video.html
+++ b/dom/canvas/test/webgl-conformance/conformance/textures/texture-npot-video.html
@@ -124,8 +124,13 @@ function runOneIteration(videoElement, useTexSubImage2D, flipY, topColor, bottom
     debug("");
 }
 
+alreadyDone = false;
 function runTest(videoElement)
 {
+    if (alreadyDone)
+        return;
+    alreadyDone = true;
+
     var red = [255, 0, 0];
     var green = [0, 255, 0];
     var black = [0, 0, 0];