diff --git a/dom/base/DOMIntersectionObserver.cpp b/dom/base/DOMIntersectionObserver.cpp
index f31b7c860ebf..6a6fd732e3ff 100644
--- a/dom/base/DOMIntersectionObserver.cpp
+++ b/dom/base/DOMIntersectionObserver.cpp
@@ -449,7 +449,8 @@ struct OopIframeMetrics {
 
 static Maybe<OopIframeMetrics> GetOopIframeMetrics(Document& aDocument,
                                                    Document* aRootDocument) {
-  Document* rootDoc = nsContentUtils::GetRootDocument(&aDocument);
+  Document* rootDoc =
+      nsContentUtils::GetInProcessSubtreeRootDocument(&aDocument);
   MOZ_ASSERT(rootDoc);
 
   if (rootDoc->IsTopLevelContentDocument()) {
@@ -457,7 +458,8 @@ static Maybe<OopIframeMetrics> GetOopIframeMetrics(Document& aDocument,
   }
 
   if (aRootDocument &&
-      rootDoc == nsContentUtils::GetRootDocument(aRootDocument)) {
+      rootDoc ==
+          nsContentUtils::GetInProcessSubtreeRootDocument(aRootDocument)) {
     // aRootDoc, if non-null, is either the implicit root
     // (top-level-content-document) or a same-origin document passed explicitly.
     //
diff --git a/dom/base/Document.cpp b/dom/base/Document.cpp
index 82836d20b03c..b5540410587a 100644
--- a/dom/base/Document.cpp
+++ b/dom/base/Document.cpp
@@ -13696,7 +13696,8 @@ bool FullscreenRoots::Contains(Document* aRoot) {
 
 /* static */
 void FullscreenRoots::Add(Document* aDoc) {
-  nsCOMPtr<Document> root = nsContentUtils::GetRootDocument(aDoc);
+  nsCOMPtr<Document> root =
+      nsContentUtils::GetInProcessSubtreeRootDocument(aDoc);
   if (!FullscreenRoots::Contains(root)) {
     if (!sInstance) {
       sInstance = new FullscreenRoots();
@@ -13722,7 +13723,8 @@ uint32_t FullscreenRoots::Find(Document* aRoot) {
 
 /* static */
 void FullscreenRoots::Remove(Document* aDoc) {
-  nsCOMPtr<Document> root = nsContentUtils::GetRootDocument(aDoc);
+  nsCOMPtr<Document> root =
+      nsContentUtils::GetInProcessSubtreeRootDocument(aDoc);
   uint32_t index = Find(root);
   NS_ASSERTION(index != NotFound,
                "Should only try to remove roots which are still added!");
@@ -13972,7 +13974,7 @@ static Document* GetFullscreenLeaf(Document* aDoc) {
   }
   // Otherwise we could be either in a non-fullscreen doc tree, or we're
   // below the fullscreen doc. Start the search from the root.
-  Document* root = nsContentUtils::GetRootDocument(aDoc);
+  Document* root = nsContentUtils::GetInProcessSubtreeRootDocument(aDoc);
   return GetFullscreenLeaf(*root);
 }
 
@@ -14632,8 +14634,9 @@ void Document::RequestFullscreenInContentProcess(
   // If we are in the content process, we can apply the fullscreen
   // state directly only if we have been in DOM fullscreen, because
   // otherwise we always need to notify the chrome.
-  if (applyFullScreenDirectly || !!nsContentUtils::GetRootDocument(this)
-                                       ->GetUnretargetedFullScreenElement()) {
+  if (applyFullScreenDirectly ||
+      !!nsContentUtils::GetInProcessSubtreeRootDocument(this)
+            ->GetUnretargetedFullScreenElement()) {
     ApplyFullscreen(std::move(aRequest));
     return;
   }
@@ -14730,7 +14733,8 @@ bool Document::ApplyFullscreen(UniquePtr<FullscreenRequest> aRequest) {
   // Remember the root document, so that if a fullscreen document is hidden
   // we can reset fullscreen state in the remaining visible fullscreen
   // documents.
-  Document* fullScreenRootDoc = nsContentUtils::GetRootDocument(this);
+  Document* fullScreenRootDoc =
+      nsContentUtils::GetInProcessSubtreeRootDocument(this);
 
   // If a document is already in fullscreen, then unlock the mouse pointer
   // before setting a new document to fullscreen
diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index 1e7859058750..5d57f9795483 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -6944,7 +6944,7 @@ void nsContentUtils::FireMutationEventsForDirectParsing(
 }
 
 /* static */
-Document* nsContentUtils::GetRootDocument(Document* aDoc) {
+Document* nsContentUtils::GetInProcessSubtreeRootDocument(Document* aDoc) {
   if (!aDoc) {
     return nullptr;
   }
diff --git a/dom/base/nsContentUtils.h b/dom/base/nsContentUtils.h
index 39932a36a9a4..a95499738ddd 100644
--- a/dom/base/nsContentUtils.h
+++ b/dom/base/nsContentUtils.h
@@ -2446,10 +2446,10 @@ class nsContentUtils {
   static bool HasPluginWithUncontrolledEventDispatch(nsIContent* aContent);
 
   /**
-   * Returns the root document in a document hierarchy. Normally this
-   * will be the chrome document.
+   * Returns the in-process subtree root document in a document hierarchy.
+   * This could be a chrome document.
    */
-  static Document* GetRootDocument(Document* aDoc);
+  static Document* GetInProcessSubtreeRootDocument(Document* aDoc);
 
   static void GetShiftText(nsAString& text);
   static void GetControlText(nsAString& text);
diff --git a/dom/base/nsFocusManager.cpp b/dom/base/nsFocusManager.cpp
index d8ebc56d7a91..b9ded5d1c25a 100644
--- a/dom/base/nsFocusManager.cpp
+++ b/dom/base/nsFocusManager.cpp
@@ -1641,7 +1641,8 @@ void nsFocusManager::SetFocusInner(Element* aNewContent, int32_t aFlags,
   // to guard against phishing.
 #ifndef XP_MACOSX
   if (elementToFocus &&
-      nsContentUtils::GetRootDocument(elementToFocus->OwnerDoc())
+      nsContentUtils::GetInProcessSubtreeRootDocument(
+          elementToFocus->OwnerDoc())
           ->GetFullscreenElement() &&
       nsContentUtils::HasPluginWithUncontrolledEventDispatch(elementToFocus)) {
     nsContentUtils::ReportToConsole(nsIScriptError::warningFlag, "DOM"_ns,
diff --git a/layout/base/GeometryUtils.cpp b/layout/base/GeometryUtils.cpp
index 04688717b3f0..aadd3f8330a6 100644
--- a/layout/base/GeometryUtils.cpp
+++ b/layout/base/GeometryUtils.cpp
@@ -327,7 +327,7 @@ void GetBoxQuadsFromWindowOrigin(nsINode* aNode,
   BoxQuadOptions bqo(aOptions);
 
   RefPtr<Document> topInProcessDoc =
-      nsContentUtils::GetRootDocument(aNode->OwnerDoc());
+      nsContentUtils::GetInProcessSubtreeRootDocument(aNode->OwnerDoc());
 
   OwningGeometryNode ogn;
   ogn.SetAsDocument() = topInProcessDoc;
diff --git a/layout/base/PresShell.cpp b/layout/base/PresShell.cpp
index 05d899547c5c..2774b16d534e 100644
--- a/layout/base/PresShell.cpp
+++ b/layout/base/PresShell.cpp
@@ -8412,7 +8412,7 @@ void PresShell::EventHandler::MaybeHandleKeyboardEventBeforeDispatch(
   Document* doc = mPresShell->GetCurrentEventContent()
                       ? mPresShell->mCurrentEventContent->OwnerDoc()
                       : nullptr;
-  Document* root = nsContentUtils::GetRootDocument(doc);
+  Document* root = nsContentUtils::GetInProcessSubtreeRootDocument(doc);
   if (root && root->GetFullscreenElement()) {
     // Prevent default action on ESC key press when exiting
     // DOM fullscreen mode. This prevents the browser ESC key