diff --git a/layout/base/nsDocumentViewer.cpp b/layout/base/nsDocumentViewer.cpp
index aa32adf61141..93a296278cc0 100644
--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -239,6 +239,9 @@ NS_IMPL_ISUPPORTS(BFCachePreventionObserver, nsIMutationObserver)
 
 void BFCachePreventionObserver::CharacterDataChanged(
     nsIContent* aContent, const CharacterDataChangeInfo&) {
+  if (aContent->IsInNativeAnonymousSubtree()) {
+    return;
+  }
   MutationHappened();
 }
 
@@ -247,19 +250,31 @@ void BFCachePreventionObserver::AttributeChanged(Element* aElement,
                                                  nsAtom* aAttribute,
                                                  int32_t aModType,
                                                  const nsAttrValue* aOldValue) {
+  if (aElement->IsInNativeAnonymousSubtree()) {
+    return;
+  }
   MutationHappened();
 }
 
 void BFCachePreventionObserver::ContentAppended(nsIContent* aFirstNewContent) {
+  if (aFirstNewContent->IsInNativeAnonymousSubtree()) {
+    return;
+  }
   MutationHappened();
 }
 
 void BFCachePreventionObserver::ContentInserted(nsIContent* aChild) {
+  if (aChild->IsInNativeAnonymousSubtree()) {
+    return;
+  }
   MutationHappened();
 }
 
 void BFCachePreventionObserver::ContentRemoved(nsIContent* aChild,
                                                nsIContent* aPreviousSibling) {
+  if (aChild->IsInNativeAnonymousSubtree()) {
+    return;
+  }
   MutationHappened();
 }
 
diff --git a/layout/base/tests/file_zoom_restore_bfcache.html b/layout/base/tests/file_zoom_restore_bfcache.html
index 17816af6bdd4..27d308bed2d3 100644
--- a/layout/base/tests/file_zoom_restore_bfcache.html
+++ b/layout/base/tests/file_zoom_restore_bfcache.html
@@ -1,8 +1,75 @@
 <!doctype html>
 <script>
+  var bcName = "zoomRestoreBfcache" + window.location.search;
+  var bc = new BroadcastChannel(bcName);
+  if (window.location.search == "?2") {
+    bc.onmessage = (msgEvent) => {
+      var msg = msgEvent.data;
+      var command = msg.command;
+      dump(`Subpage ?2 received command=${command}\n`);
+      switch (command) {
+        case "case2sendData": {
+          bc.postMessage({command: "case2data", devicePixelRatio: window.devicePixelRatio,
+            frameDevicePixelRatio: document.querySelector("iframe").contentWindow.devicePixelRatio});
+          break;
+        }
+        case "case2action": {
+          SpecialPowers.spawnChrome([], () => {
+            const FullZoom = this.browsingContext.embedderElement.ownerGlobal.FullZoom;
+            FullZoom.setZoom(2.0);
+          });
+          SpecialPowers.setFullZoom(window, 2);
+          window.requestAnimationFrame(() => window.requestAnimationFrame(() => {
+            bc.postMessage({command: "case2dataAnimationFrame", devicePixelRatio: window.devicePixelRatio,
+            frameDevicePixelRatio: document.querySelector("iframe").contentWindow.devicePixelRatio });
+          }));
+          break;
+        }
+        case "case2back": {
+          bc.close();
+          window.history.back();
+          break;
+        }
+      }
+    }
+  } else {
+    bc.onmessage = (msgEvent) => {
+      var msg = msgEvent.data;
+      var command = msg.command;
+      dump(`Subpage received command=${command}\n`);
+      switch (command) {
+        case "case1sendData": {
+          bc.postMessage({command: "case1data", devicePixelRatio: window.devicePixelRatio});
+          break;
+        }
+        case "case1click": {
+          document.querySelector("a").click();
+          // We are opening file_zoom_restore_bfcache.html?2, so the current
+          // page is going into bfcache
+          break;
+        }
+        case "case3sendData": {
+          // We came back from bfcache
+          bc.postMessage({command: "case3data", devicePixelRatio: window.devicePixelRatio,
+            frameDevicePixelRatio: document.querySelector("iframe").contentWindow.devicePixelRatio});
+          break;
+        }
+        case "close": {
+          SpecialPowers.spawnChrome([], () => {
+            const FullZoom = this.browsingContext.embedderElement.ownerGlobal.FullZoom;
+            FullZoom.setZoom(1.0);
+          });
+          bc.postMessage({command: "closed"});
+          bc.close();
+          window.close();
+          break;
+        }
+      }
+    }
+  }
   window.addEventListener("pageshow", function(e) {
-    window.opener.handlePageShow(e.persisted);
+    bc.postMessage({command: "handlePageShow", eventPersisted: e.persisted});
   });
 </script>
-<a href="?1">This is a very interesting page</a>
+<a href="?2">This is a very interesting page</a>
 <iframe srcdoc="And this is a nested frame"></iframe>
diff --git a/layout/base/tests/test_zoom_restore_bfcache.html b/layout/base/tests/test_zoom_restore_bfcache.html
index debac3ee2cfb..ffe158f220b4 100644
--- a/layout/base/tests/test_zoom_restore_bfcache.html
+++ b/layout/base/tests/test_zoom_restore_bfcache.html
@@ -7,34 +7,117 @@
 <script>
 SimpleTest.waitForExplicitFinish();
 
+/**
+ * - main page (this one) opens file_zoom_restore_bfcache.html
+ * - file_zoom_restore_bfcache.html sends "handlePageShow" to main page
+ * - main page sends file_zoom_restore_bfcache.html "case1sendData"
+ * - file_zoom_restore_bfcache.html sends "case1data" to main page
+ * - main page sends "case1click" to file_zoom_restore_bfcache.html
+ * - file_zoom_restore_bfcache.html clicks on <a> element, navigating to uri
+ *   file_zoom_restore_bfcache.html?2, and gets bfcached
+ * - file_zoom_restore_bfcache.html?2 sends "handlePageShow" to main page
+ * - main page sends "case2sendData" to file_zoom_restore_bfcache.html?2
+ * - file_zoom_restore_bfcache.html?2 sends "case2data" to main page
+ * - main page sends "case2action" to file_zoom_restore_bfcache.html?2
+ * - file_zoom_restore_bfcache.html?2 sends "case2dataAnimationFrame" to main page
+ * - main page sends "case2back" to file_zoom_restore_bfcache.html?2
+ * - file_zoom_restore_bfcache.html?2 navigates back to file_zoom_restore_bfcache.html
+ * - file_zoom_restore_bfcache.html sends "handlePageShow" to main page
+ * - main page sends "case3sendData to file_zoom_restore_bfcache.html
+ * - file_zoom_restore_bfcache.html sends "case3data" to main page
+ * - main page sends "close to file_zoom_restore_bfcache.html
+ * - file_zoom_restore_bfcache.html closes bc and window and sends back "closed"
+ **/
+
 const originalDPR = window.devicePixelRatio;
 let loadCount = 0;
-let childWin;
+var bc = new BroadcastChannel("zoomRestoreBfcache");
+var bcPage2 = new BroadcastChannel("zoomRestoreBfcache?2");
+bc.onmessage = (msgEvent) => {
+  var msg = msgEvent.data;
+  var command = msg.command;
+  info(`Main page, received command from normal bc=${command}`);
+  switch (command) {
+    case "handlePageShow": {
+      handlePageShow(msgEvent.data.eventPersisted);
+      break;
+    }
+    case "case1data": {
+      is(loadCount, 1, "Case 1");
+      is(msg.devicePixelRatio, originalDPR, "No zoom");
+      bc.postMessage({command: "case1click"});
+      // The end of case 1
+      break;
+    }
+    case "case3data": {
+      is(loadCount, 2, "Case 3");
+      is(msg.devicePixelRatio, originalDPR * 2, "Should preserve zoom when restored");
+      todo_is(msg.frameDevicePixelRatio, originalDPR * 2, "Should preserve zoom on frames too");
+      bc.postMessage({command: "close"});
+      // Now we wait for "closed"
+      break;
+    }
+    case "closed": {
+      is(loadCount, 2, "Case 3");
+      bc.close();
+      SimpleTest.finish();
+      break;
+    }
+    default:
+      ok(false, "should not receive extra messages via BroadcastChannel");
+  }
+}
+bcPage2.onmessage = (msgEvent) => {
+  var msg = msgEvent.data;
+  var command = msg.command;
+  info(`Main page, received command from bc?2=${command}`);
+  switch (command) {
+    case "handlePageShow": {
+      handlePageShow(msgEvent.data.eventPersisted);
+      break;
+    }
+    case "case2data": {
+      is(loadCount, 2, "Case 2");
+      is(msg.devicePixelRatio, originalDPR, "No zoom (yet)")
+      is(msg.frameDevicePixelRatio, originalDPR, "No zoom on frame either");
+      bcPage2.postMessage({command: "case2action"});
+      // Now we wait for "case2dataAnimationFrame"
+      break;
+    }
+    case "case2dataAnimationFrame": {
+      is(loadCount, 2, "Case 2");
+      is(msg.devicePixelRatio, originalDPR * 2, "Zoomed");
+      is(msg.frameDevicePixelRatio, originalDPR * 2, "Zoomed iframe too");
+      bcPage2.postMessage({command: "case2back"});
+      bcPage2.close();
+      // The end of case 2
+      break;
+    }
+    default:
+      ok(false, "should not receive extra messages via BroadcastChannel");
+  }
+}
 function handlePageShow(persisted) {
   ok(typeof persisted == "boolean", "Should get the persisted state from the pageshow event");
-  is(persisted, loadCount == 2, "Should've gone into the bfcache after the back navigation");
+  if (loadCount == 2) {
+    ok(persisted,  "Should've gone into the bfcache after the back navigation");
+  } else {
+    ok(!persisted,  "Should NOT be retrieved from bfcache");
+  }
 
   if (loadCount == 0) {
     loadCount++;
-    is(childWin.devicePixelRatio, originalDPR, "No zoom")
-    childWin.document.querySelector("a").click(); // navigate away
+    bc.postMessage({command: "case1sendData"});
+    // Now we wait for the "case1data" message
   } else if (loadCount == 1) {
     loadCount++;
-    is(childWin.devicePixelRatio, originalDPR, "No zoom (yet)")
-    is(childWin.document.querySelector("iframe").contentWindow.devicePixelRatio, originalDPR, "No zoom on frame either");
-    SpecialPowers.setFullZoom(childWin, 2);
-    childWin.requestAnimationFrame(() => childWin.requestAnimationFrame(() => {
-      is(childWin.devicePixelRatio, originalDPR * 2, "Zoomed");
-      is(childWin.document.querySelector("iframe").contentWindow.devicePixelRatio, originalDPR * 2, "Zoomed iframe too");
-      childWin.history.back();
-    }));
+    bcPage2.postMessage({command: "case2sendData"});
+    // Now we wait for the "case2data" message
   } else {
-    is(childWin.devicePixelRatio, originalDPR * 2, "Should preserve zoom when restored");
-    todo_is(childWin.document.querySelector("iframe").contentWindow.devicePixelRatio, originalDPR * 2, "Should preserve zoom on frames too");
-    childWin.close();
-    SimpleTest.finish();
+    bc.postMessage({command: "case3sendData"});
+    // Now we wait for the "case3data" message
   }
 }
 
-childWin = window.open('file_zoom_restore_bfcache.html', '_blank');
+window.open('file_zoom_restore_bfcache.html', '_blank', 'noopener');
 </script>
