--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -1505,18 +1505,25 @@ nsIDocument::nsIDocument()
     mValidHeight(false),
     mAutoSize(false),
     mAllowZoom(false),
     mAllowDoubleTapZoom(false),
     mValidScaleFloat(false),
     mValidMaxScale(false),
     mScaleStrEmpty(false),
     mWidthStrEmpty(false),
+    mParserAborted(false),
+    mReportedUseCounters(false),
+#ifdef DEBUG
+    mWillReparent(false),
+#endif
     mPendingFullscreenRequests(0),
     mXMLDeclarationBits(0),
+    mOnloadBlockCount(0),
+    mAsyncOnloadBlockCount(0),
     mCompatMode(eCompatibility_FullStandards),
     mReadyState(ReadyState::READYSTATE_UNINITIALIZED),
     mStyleBackendType(StyleBackendType::None),
 #ifdef MOZILLA_INTERNAL_API
     mVisibilityState(dom::VisibilityState::Hidden),
 #else
     mDummy(0),
 #endif
@@ -1560,23 +1567,16 @@ nsIDocument::nsIDocument()
   SetIsInDocument();
   for (auto& cnt : mIncCounters) {
     cnt = 0;
   }
 }
 
 nsDocument::nsDocument(const char* aContentType)
   : nsIDocument()
-  , mParserAborted(false)
-  , mReportedUseCounters(false)
-  , mOnloadBlockCount(0)
-  , mAsyncOnloadBlockCount(0)
-#ifdef DEBUG
-  , mWillReparent(false)
-#endif
 {
   SetContentTypeInternal(nsDependentCString(aContentType));
 
   MOZ_LOG(gDocumentLeakPRLog, LogLevel::Debug, ("DOCUMENT %p created", this));
 
   // Start out mLastStyleSheetSet as null, per spec
   SetDOMStringToNull(mLastStyleSheetSet);
 

--- a/dom/base/nsDocument.h
+++ b/dom/base/nsDocument.h
@@ -335,30 +335,18 @@ public:
   // cause nsIDocument's layout to be wrong in the Rust side.
   //
   // This can be fixed after updating to rust 1.25 and updating bindgen to
   // include https://github.com/rust-lang-nursery/rust-bindgen/pull/1271.
   js::ExpandoAndGeneration mExpandoAndGeneration;
 
   nsClassHashtable<nsStringHashKey, nsRadioGroupStruct> mRadioGroups;
 
-  // Parser aborted. True if the parser of this document was forcibly
-  // terminated instead of letting it finish at its own pace.
-  bool mParserAborted:1;
-
   friend class nsCallRequestFullScreen;
 
-  // Whether we have reported use counters for this document with Telemetry yet.
-  // Normally this is only done at document destruction time, but for image
-  // documents (SVG documents) that are not guaranteed to be destroyed, we
-  // report use counters when the image cache no longer has any imgRequestProxys
-  // pointing to them.  We track whether we ever reported use counters so
-  // that we only report them once for the document.
-  bool mReportedUseCounters:1;
-
   // The application cache that this document is associated with, if
   // any.  This can change during the lifetime of the document.
   nsCOMPtr<nsIApplicationCache> mApplicationCache;
 
   nsCOMPtr<nsIContent> mFirstBaseNodeWithHref;
 private:
   friend class nsUnblockOnloadEvent;
 
@@ -367,29 +355,16 @@ private:
 
   nsresult InitCSP(nsIChannel* aChannel);
 
   void ClearAllBoxObjects();
 
   // These are not implemented and not supported.
   nsDocument(const nsDocument& aOther);
   nsDocument& operator=(const nsDocument& aOther);
-
-  // Currently active onload blockers
-  uint32_t mOnloadBlockCount;
-  // Onload blockers which haven't been activated yet
-  uint32_t mAsyncOnloadBlockCount;
-  nsCOMPtr<nsIRequest> mOnloadBlocker;
-
-  nsCOMPtr<nsIRunnable> mMaybeEndOutermostXBLUpdateRunner;
-
-#ifdef DEBUG
-public:
-  bool mWillReparent;
-#endif
 };
 
 class nsDocumentOnStack
 {
 public:
   explicit nsDocumentOnStack(nsIDocument* aDoc) : mDoc(aDoc)
   {
     mDoc->IncreaseStackRefCnt();

--- a/dom/base/nsIDocument.h
+++ b/dom/base/nsIDocument.h
@@ -4167,20 +4167,44 @@ protected:
   bool mAutoSize: 1;
   bool mAllowZoom: 1;
   bool mAllowDoubleTapZoom: 1;
   bool mValidScaleFloat: 1;
   bool mValidMaxScale: 1;
   bool mScaleStrEmpty: 1;
   bool mWidthStrEmpty: 1;
 
+  // Parser aborted. True if the parser of this document was forcibly
+  // terminated instead of letting it finish at its own pace.
+  bool mParserAborted: 1;
+
+  // Whether we have reported use counters for this document with Telemetry yet.
+  // Normally this is only done at document destruction time, but for image
+  // documents (SVG documents) that are not guaranteed to be destroyed, we
+  // report use counters when the image cache no longer has any imgRequestProxys
+  // pointing to them.  We track whether we ever reported use counters so
+  // that we only report them once for the document.
+  bool mReportedUseCounters: 1;
+
+#ifdef DEBUG
+public:
+  bool mWillReparent: 1;
+protected:
+#endif
+
   uint8_t mPendingFullscreenRequests;
 
   uint8_t mXMLDeclarationBits;
 
+  // Currently active onload blockers.
+  uint32_t mOnloadBlockCount;
+
+  // Onload blockers which haven't been activated yet.
+  uint32_t mAsyncOnloadBlockCount;
+
   // Compatibility mode
   nsCompatibility mCompatMode;
 
   // Our readyState
   ReadyState mReadyState;
 
   // Whether this document has (or will have, once we have a pres shell) a
   // Gecko- or Servo-backed style system.
@@ -4492,16 +4516,19 @@ protected:
   mozilla::LayoutDeviceToScreenScale mScaleMinFloat;
   mozilla::LayoutDeviceToScreenScale mScaleMaxFloat;
   mozilla::LayoutDeviceToScreenScale mScaleFloat;
   mozilla::CSSToLayoutDeviceScale mPixelRatio;
   mozilla::CSSSize mViewportSize;
 
   RefPtr<mozilla::EventListenerManager> mListenerManager;
 
+  nsCOMPtr<nsIRunnable> mMaybeEndOutermostXBLUpdateRunner;
+  nsCOMPtr<nsIRequest> mOnloadBlocker;
+
   nsTArray<RefPtr<mozilla::StyleSheet>> mOnDemandBuiltInUASheets;
   nsTArray<RefPtr<mozilla::StyleSheet>> mAdditionalSheets[AdditionalSheetTypeCount];
 
   // Member to store out last-selected stylesheet set.
   nsString mLastStyleSheetSet;
   RefPtr<nsDOMStyleSheetSetList> mStyleSheetSetList;
 
   // We lazily calculate declaration blocks for SVG elements with mapped

--- a/dom/html/nsHTMLDocument.cpp
+++ b/dom/html/nsHTMLDocument.cpp
@@ -1425,18 +1425,17 @@ nsHTMLDocument::Open(JSContext* cx,
   if (nsPIDOMWindowInner *window = GetInnerWindow()) {
     // Remember the old scope in case the call to SetNewDocument changes it.
     nsCOMPtr<nsIScriptGlobalObject> oldScope(do_QueryReferent(mScopeObject));
 
 #ifdef DEBUG
     bool willReparent = mWillReparent;
     mWillReparent = true;
 
-    nsDocument* templateContentsOwner =
-      static_cast<nsDocument*>(mTemplateContentsOwner.get());
+    nsIDocument* templateContentsOwner = mTemplateContentsOwner.get();
 
     if (templateContentsOwner) {
       templateContentsOwner->mWillReparent = true;
     }
 #endif
 
     // Set our ready state to uninitialized before setting the new document so
     // that window creation listeners don't use the document in its intermediate