--- a/docshell/base/nsDocShell.cpp
+++ b/docshell/base/nsDocShell.cpp
@@ -8696,29 +8696,33 @@ nsDocShell::RestoreFromHistory()
   // Save off the root view's parent and sibling so that we can insert the
   // new content viewer's root view at the same position.  Also save the
   // bounds of the root view's widget.
 
   nsView* rootViewSibling = nullptr;
   nsView* rootViewParent = nullptr;
   nsIntRect newBounds(0, 0, 0, 0);
 
+  // Also save whether global font scaling was active on the previous shell.
+  bool globalZoomState = false;
+
   nsCOMPtr<nsIPresShell> oldPresShell = GetPresShell();
   if (oldPresShell) {
     nsViewManager* vm = oldPresShell->GetViewManager();
     if (vm) {
       nsView* oldRootView = vm->GetRootView();
 
       if (oldRootView) {
         rootViewSibling = oldRootView->GetNextSibling();
         rootViewParent = oldRootView->GetParent();
 
         mContentViewer->GetBounds(newBounds);
       }
     }
+    globalZoomState = oldPresShell->GetGlobalZoomState();
   }
 
   nsCOMPtr<nsIContent> container;
   nsCOMPtr<nsIDocument> sibling;
   if (rootViewParent && rootViewParent->GetParent()) {
     nsIFrame* frame = rootViewParent->GetParent()->GetFrame();
     container = frame ? frame->GetContent() : nullptr;
   }
@@ -9058,16 +9062,17 @@ nsDocShell::RestoreFromHistory()
   newRootView = rootViewSibling = rootViewParent = nullptr;
   newVM = nullptr;
 
   // Simulate the completion of the load.
   nsDocShell::FinishRestore();
 
   // Restart plugins, and paint the content.
   if (shell) {
+    shell->SetGlobalZoomState(globalZoomState);
     shell->Thaw();
   }
 
   return privWin->FireDelayedDOMEvents();
 }
 
 nsresult
 nsDocShell::CreateContentViewer(const nsACString& aContentType,
@@ -9391,30 +9396,33 @@ nsDocShell::SetupNewViewer(nsIContentVie
                           NS_ERROR_FAILURE);
         NS_ENSURE_SUCCESS(oldCv->GetAuthorStyleDisabled(&styleDisabled),
                           NS_ERROR_FAILURE);
       }
     }
   }
 
   nscolor bgcolor = NS_RGBA(0, 0, 0, 0);
+  bool globalZoomState = false;
   // Ensure that the content viewer is destroyed *after* the GC - bug 71515
   nsCOMPtr<nsIContentViewer> contentViewer = mContentViewer;
   if (contentViewer) {
     // Stop any activity that may be happening in the old document before
     // releasing it...
     contentViewer->Stop();
 
     // Try to extract the canvas background color from the old
     // presentation shell, so we can use it for the next document.
     nsCOMPtr<nsIPresShell> shell;
     contentViewer->GetPresShell(getter_AddRefs(shell));
 
     if (shell) {
       bgcolor = shell->GetCanvasBackground();
+      // Also copy the global zoom state over.
+      globalZoomState = shell->GetGlobalZoomState();
     }
 
     contentViewer->Close(mSavingOldViewer ? mOSHE.get() : nullptr);
     aNewViewer->SetPreviousViewer(contentViewer);
   }
   if (mOSHE && (!mContentViewer || !mSavingOldViewer)) {
     // We don't plan to save a viewer in mOSHE; tell it to drop
     // any other state it's holding.
@@ -9465,16 +9473,17 @@ nsDocShell::SetupNewViewer(nsIContentVie
 
   // Stuff the bgcolor from the old pres shell into the new
   // pres shell. This improves page load continuity.
   nsCOMPtr<nsIPresShell> shell;
   mContentViewer->GetPresShell(getter_AddRefs(shell));
 
   if (shell) {
     shell->SetCanvasBackground(bgcolor);
+    shell->SetGlobalZoomState(globalZoomState);
   }
 
   // XXX: It looks like the LayoutState gets restored again in Embed()
   //      right after the call to SetupNewViewer(...)
 
   // We don't show the mContentViewer yet, since we want to draw the old page
   // until we have enough of the new page to show.  Just return with the new
   // viewer still set to hidden.

--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -836,16 +836,17 @@ TransferZoomLevels(nsIDocument* aFromDoc
   nsPresContext* toCtxt = toShell->GetPresContext();
   if (!toCtxt)
     return;
 
   toCtxt->SetFullZoom(fromCtxt->GetFullZoom());
   toCtxt->SetBaseMinFontSize(fromCtxt->BaseMinFontSize());
   toCtxt->SetTextZoom(fromCtxt->TextZoom());
   toCtxt->SetOverrideDPPX(fromCtxt->GetOverrideDPPX());
+  toShell->SetGlobalZoomState(fromShell->GetGlobalZoomState());
 }
 
 void
 TransferShowingState(nsIDocument* aFromDoc, nsIDocument* aToDoc)
 {
   MOZ_ASSERT(aFromDoc && aToDoc,
              "transferring showing state from/to null doc");
 

--- a/layout/base/nsIPresShell.h
+++ b/layout/base/nsIPresShell.h
@@ -1591,16 +1591,19 @@ public:
    * whether font size inflation is enabled on the next call to
    * FontSizeInflationEnabled().
    */
   void NotifyFontSizeInflationEnabledIsDirty()
   {
     mFontSizeInflationEnabledIsDirty = true;
   }
 
+  void SetGlobalZoomState(bool aEnabled) { mGlobalZoomWasEnabled = aEnabled; }
+  bool GetGlobalZoomState() { return mGlobalZoomWasEnabled; }
+
   virtual void AddInvalidateHiddenPresShellObserver(nsRefreshDriver *aDriver) = 0;
 
   void InvalidatePresShellIfHidden();
   void CancelInvalidatePresShellIfHidden();
 
 
   //////////////////////////////////////////////////////////////////////////////
   // Approximate frame visibility tracking public API.