diff --git a/js/content-script.js b/js/content-script.js
index d287825..33971df 100644
--- a/js/content-script.js
+++ b/js/content-script.js
@@ -554,8 +554,7 @@ function restoreVideo() {
 
   let mvClassList = [mvImpl.mvClass, 'core'];
   for(let cn of mvClassList) {
-    let nodes = document.querySelectorAll('[mvclass='+cn+']');
-    for(let node of nodes) {
+    for(let { elem: node } of deepQueryAll('[mvclass='+cn+']')) {
       node.removeAttribute('mvclass');
     }
   }
@@ -608,19 +607,40 @@ function maximizeVideo(selectedNode, chain = []) {
   maximizeMainNode();
 }
 
+// Collect every element matching `selector`, including elements inside open
+// shadow roots (e.g. the <youtube-video> web component that learn.udacity.com
+// uses to host its YouTube iframe). Each result carries the chain of shadow
+// hosts (outermost first) so callers can walk back out of the shadow tree,
+// matching the `chain` convention used by findVideoElement()/maximizeVideo().
+function deepQueryAll(selector, root = document, chain = []) {
+  const results = [];
+  root.querySelectorAll(selector).forEach(elem => {
+    results.push({ elem: elem, chain: [...chain] });
+  });
+  root.querySelectorAll('*').forEach(elem => {
+    if (elem.shadowRoot) {
+      results.push(...deepQueryAll(selector, elem.shadowRoot, [...chain, elem]));
+    }
+  });
+  return results;
+}
+
+function getAllIFrames() {
+  return deepQueryAll('iframe');
+}
+
 function getChildIFrameById(id) {
-  let iframes = document.getElementsByTagName('IFRAME');
-  for(let iframe of iframes) {
-    if(iframe.getAttribute('mv_iframe') === id) {
-      return iframe;
+  for(let info of getAllIFrames()) {
+    if(info.elem.getAttribute('mv_iframe') === id) {
+      return info;
     }
   }
+  return { elem: null, chain: [] };
 }
 
 window.addEventListener('message', e => {
   if (e.data.action === 'getId') { //message from child
-    let iframes = document.getElementsByTagName('IFRAME');
-    for(let iframe of iframes) {
+    for(let { elem: iframe } of getAllIFrames()) {
       let vmi = iframe.getAttribute('mv_iframe');
       if(!vmi) {
         iframe.setAttribute('mv_iframe', idCount);
@@ -647,20 +667,22 @@ window.addEventListener('message', e => {
     }
   }
   else if(e.data.action === 'setVideoNode'){ //message from child
-    let iframe = getChildIFrameById(e.data.id);
+    let { elem: iframe, chain } = getChildIFrameById(e.data.id);
+    if(!iframe) return;
     let hashCode = iframe.getAttribute('mvHashCode');
     if(!hashCode) {
       hashCode = getHashCode(HASHCODE_LENGTH);
       iframe.setAttribute('mvHashCode', hashCode);
     }
     mvImpl.currentHashCode = hashCode;
-    maximizeVideo(iframe);
+    maximizeVideo(iframe, chain);
     // if(window !== window.top) {
     //   window.parent.postMessage({action: 'getId', senderId: selfId, nextAction: 'setVideoNode'},'*');
     // }
   }
   else if(e.data.action === 'addVideoElements'){ //message from child
-    let iframe = getChildIFrameById(e.data.id);
+    let { elem: iframe } = getChildIFrameById(e.data.id);
+    if(!iframe) return;
     let iframeRect = iframe.getBoundingClientRect();
     if(window !== window.top) {
       for(let elemInfo of e.data.elemInfos) {