diff --git a/layout/base/AccessibleCaret.cpp b/layout/base/AccessibleCaret.cpp
index 35bc98c70c6..6abe096e94f 100644
--- a/layout/base/AccessibleCaret.cpp
+++ b/layout/base/AccessibleCaret.cpp
@@ -57,13 +57,14 @@ AccessibleCaret::AccessibleCaret(nsIPresShell* aPresShell)
   : mPresShell(aPresShell)
 {
   // Check all resources required.
-  MOZ_ASSERT(mPresShell);
-  MOZ_ASSERT(RootFrame());
-  MOZ_ASSERT(mPresShell->GetDocument());
-  MOZ_ASSERT(mPresShell->GetCanvasFrame());
-  MOZ_ASSERT(mPresShell->GetCanvasFrame()->GetCustomContentContainer());
+  if (mPresShell) {
+    MOZ_ASSERT(RootFrame());
+    MOZ_ASSERT(mPresShell->GetDocument());
+    MOZ_ASSERT(mPresShell->GetCanvasFrame());
+    MOZ_ASSERT(mPresShell->GetCanvasFrame()->GetCustomContentContainer());
 
-  InjectCaretElement(mPresShell->GetDocument());
+    InjectCaretElement(mPresShell->GetDocument());
+  }
 
   static bool prefsAdded = false;
   if (!prefsAdded) {
@@ -77,7 +78,9 @@ AccessibleCaret::AccessibleCaret(nsIPresShell* aPresShell)
 
 AccessibleCaret::~AccessibleCaret()
 {
-  RemoveCaretElement(mPresShell->GetDocument());
+  if (mPresShell) {
+    RemoveCaretElement(mPresShell->GetDocument());
+  }
 }
 
 void
diff --git a/layout/base/AccessibleCaret.h b/layout/base/AccessibleCaret.h
index c4b49ccfc18..feb24f5691f 100644
--- a/layout/base/AccessibleCaret.h
+++ b/layout/base/AccessibleCaret.h
@@ -37,11 +37,11 @@ namespace mozilla {
 // that SetPosition() works correctly, the caller must make sure the layout is
 // up to date.
 //
-class AccessibleCaret final
+class AccessibleCaret
 {
 public:
   explicit AccessibleCaret(nsIPresShell* aPresShell);
-  ~AccessibleCaret();
+  virtual ~AccessibleCaret();
 
   // This enumeration representing the visibility and visual style of an
   // AccessibleCaret.
@@ -74,7 +74,7 @@ public:
     return mAppearance;
   }
 
-  void SetAppearance(Appearance aAppearance);
+  virtual void SetAppearance(Appearance aAppearance);
 
   // Return true if current appearance is either Normal, NormalNotShown, Left,
   // or Right.
@@ -92,7 +92,7 @@ public:
 
   // Set true to enable the "Text Selection Bar" described in "Text Selection
   // Visual Spec" in bug 921965.
-  void SetSelectionBarEnabled(bool aEnabled);
+  virtual void SetSelectionBarEnabled(bool aEnabled);
 
   // This enumeration representing the result returned by SetPosition().
   enum class PositionChangedResult : uint8_t {
@@ -105,7 +105,7 @@ public:
     // Position is out of scroll port.
     Invisible
   };
-  PositionChangedResult SetPosition(nsIFrame* aFrame, int32_t aOffset);
+  virtual PositionChangedResult SetPosition(nsIFrame* aFrame, int32_t aOffset);
 
   // Does two AccessibleCarets overlap?
   bool Intersects(const AccessibleCaret& aCaret) const;
@@ -127,7 +127,7 @@ public:
     return mCaretElementHolder->GetContentNode();
   }
 
-private:
+protected:
   // Argument aRect should be relative to CustomContentContainerFrame().
   void SetCaretElementStyle(const nsRect& aRect);
   void SetSelectionBarElementStyle(const nsRect& aRect);