diff --git a/dom/base/Document.cpp b/dom/base/Document.cpp
index 372c1a36ab06..8f139475c2e3 100644
--- a/dom/base/Document.cpp
+++ b/dom/base/Document.cpp
@@ -13166,16 +13166,18 @@ class PendingFullscreenChangeList {
   class Iterator {
    public:
     explicit Iterator(Document* aDoc, IteratorOption aOption)
-        : mCurrent(PendingFullscreenChangeList::sList.getFirst()),
-          mRootShellForIteration(aDoc->GetDocShell()) {
+        : mCurrent(PendingFullscreenChangeList::sList.getFirst()) {
       if (mCurrent) {
-        if (mRootShellForIteration && aOption == eDocumentsWithSameRoot) {
-          // Use a temporary to avoid undefined behavior from passing
-          // mRootShellForIteration.
-          nsCOMPtr<nsIDocShellTreeItem> root;
-          mRootShellForIteration->GetInProcessRootTreeItem(
-              getter_AddRefs(root));
-          mRootShellForIteration = std::move(root);
+        if (aDoc->GetBrowsingContext()) {
+          mRootBCForIteration = aDoc->GetBrowsingContext();
+          if (aOption == eDocumentsWithSameRoot) {
+            RefPtr<BrowsingContext> bc =
+                GetParentIgnoreChromeBoundary(mRootBCForIteration);
+            while (bc) {
+              mRootBCForIteration = bc;
+              bc = GetParentIgnoreChromeBoundary(mRootBCForIteration);
+            }
+          }
         }
         SkipToNextMatch();
       }
@@ -13189,6 +13191,16 @@ class PendingFullscreenChangeList {
     bool AtEnd() const { return mCurrent == nullptr; }
 
    private:
+    already_AddRefed<BrowsingContext> GetParentIgnoreChromeBoundary(
+        BrowsingContext* aBC) {
+      // Chrome BrowsingContexts are only available in the parent process, so if
+      // we're in a content process, we only worry about the context tree.
+      if (XRE_IsParentProcess()) {
+        return aBC->Canonical()->GetParentCrossChromeBoundary();
+      }
+      return do_AddRef(aBC->GetParent());
+    }
+
     UniquePtr<T> TakeAndNextInternal() {
       FullscreenChange* thisChange = mCurrent;
       MOZ_ASSERT(thisChange->Type() == T::kType);
@@ -13198,21 +13210,19 @@ class PendingFullscreenChangeList {
     void SkipToNextMatch() {
       while (mCurrent) {
         if (mCurrent->Type() == T::kType) {
-          nsCOMPtr<nsIDocShellTreeItem> docShell =
-              mCurrent->Document()->GetDocShell();
-          if (!docShell) {
+          RefPtr<BrowsingContext> bc =
+              mCurrent->Document()->GetBrowsingContext();
+          if (!bc) {
             // Always automatically drop fullscreen changes which are
             // from a document detached from the doc shell.
             UniquePtr<T> change = TakeAndNextInternal();
             change->MayRejectPromise("Document is not active");
             continue;
           }
-          while (docShell && docShell != mRootShellForIteration) {
-            nsCOMPtr<nsIDocShellTreeItem> parent;
-            docShell->GetInProcessParent(getter_AddRefs(parent));
-            docShell = std::move(parent);
+          while (bc && bc != mRootBCForIteration) {
+            bc = GetParentIgnoreChromeBoundary(bc);
           }
-          if (docShell) {
+          if (bc) {
             break;
           }
         }
@@ -13223,7 +13233,7 @@ class PendingFullscreenChangeList {
     }
 
     FullscreenChange* mCurrent;
-    nsCOMPtr<nsIDocShellTreeItem> mRootShellForIteration;
+    RefPtr<BrowsingContext> mRootBCForIteration;
   };
 
  private:
@@ -13966,6 +13976,7 @@ bool Document::FullscreenElementReadyCheck(FullscreenRequest& aRequest) {
 }
 
 static nsCOMPtr<nsPIDOMWindowOuter> GetRootWindow(Document* aDoc) {
+  MOZ_ASSERT(XRE_IsParentProcess());
   nsIDocShell* docShell = aDoc->GetDocShell();
   if (!docShell) {
     return nullptr;