Fix firefox iframe timing issue, fixes #25

src/Layout-test-utils.js

@@ -44,17 +44,23 @@ var layoutTestUtils = (function() {
     };
   }
 
+  function renderIframe() {
+    var iframe = document.createElement('iframe');
+    document.body.appendChild(iframe);
+    return iframe;
+  }
+
   var cachedIframe;
   function getIframe() {
     if (cachedIframe) {
       return cachedIframe;
     }
-    var iframe = document.createElement('iframe');
-    document.body.appendChild(iframe);
+
     var doc = iframe.contentDocument;
 
+    if(doc.readyState === 'complete') {
       var style = document.createElement('style');
-    style.innerText = (function() {/*
+      style.textContent = (function() {/*
         body, div {
           box-sizing: border-box;
           border: 0 solid black;
@@ -83,8 +89,15 @@ var layoutTestUtils = (function() {
       doc.head.appendChild(style);
       cachedIframe = iframe;
       return iframe;
+    } else {
+      setTimeout(getIframe, 0);
+    }
   }
 
+  if (typeof window !== 'undefined') {
+    var iframe = renderIframe();
+    getIframe();
+  }
 
   if (typeof computeLayout === 'function') {
     var realComputeLayout = computeLayout;