diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index 95115ed11934..708ca29b3103 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -3254,21 +3254,6 @@ nsIDocument::HasFocus(ErrorResult& rv) const
   return false;
 }
 
-TimeStamp
-nsIDocument::LastFocusTime() const
-{
-  return mLastFocusTime;
-}
-
-void
-nsIDocument::SetLastFocusTime(const TimeStamp& aFocusTime)
-{
-  MOZ_DIAGNOSTIC_ASSERT(!aFocusTime.IsNull());
-  MOZ_DIAGNOSTIC_ASSERT(mLastFocusTime.IsNull() ||
-                        aFocusTime >= mLastFocusTime);
-  mLastFocusTime = aFocusTime;
-}
-
 NS_IMETHODIMP
 nsDocument::GetReferrer(nsAString& aReferrer)
 {
@@ -4768,14 +4753,6 @@ nsDocument::SetScriptGlobalObject(nsIScriptGlobalObject *aScriptGlobalObject)
     }
 
     MaybeRescheduleAnimationFrameNotifications();
-
-    // If we are set in a window that is already focused we should remember this
-    // as the time the document gained focus.
-    bool focused = false;
-    Unused << HasFocus(&focused);
-    if (focused) {
-      SetLastFocusTime(TimeStamp::Now());
-    }
   }
 
   // Remember the pointer to our window (or lack there of), to avoid
diff --git a/dom/base/nsFocusManager.cpp b/dom/base/nsFocusManager.cpp
index d18574e71e45..ad1bf6c95306 100644
--- a/dom/base/nsFocusManager.cpp
+++ b/dom/base/nsFocusManager.cpp
@@ -3611,17 +3611,6 @@ nsFocusManager::SetFocusedWindowInternal(nsPIDOMWindowOuter* aWindow)
     nsCOMPtr<nsIRunnable> runnable = new PointerUnlocker();
     NS_DispatchToCurrentThread(runnable);
   }
-
-  // Update the last focus time on any affected documents
-  if (aWindow && aWindow != mFocusedWindow) {
-    const TimeStamp now(TimeStamp::Now());
-    for (nsIDocument* doc = aWindow->GetExtantDoc();
-         doc;
-         doc = doc->GetParentDocument()) {
-      doc->SetLastFocusTime(now);
-    }
-  }
-
   mFocusedWindow = aWindow;
 }
 
diff --git a/dom/base/nsIDocument.h b/dom/base/nsIDocument.h
index d5c2f59f6889..6bd5d2259576 100644
--- a/dom/base/nsIDocument.h
+++ b/dom/base/nsIDocument.h
@@ -2656,8 +2656,6 @@ public:
   }
   Element* GetActiveElement();
   bool HasFocus(mozilla::ErrorResult& rv) const;
-  mozilla::TimeStamp LastFocusTime() const;
-  void SetLastFocusTime(const mozilla::TimeStamp& aFocusTime);
   // Event handlers are all on nsINode already
   bool MozSyntheticDocument() const
   {
@@ -3027,10 +3025,6 @@ protected:
   // container for per-context fonts (downloadable, SVG, etc.)
   RefPtr<mozilla::dom::FontFaceSet> mFontFaceSet;
 
-  // Last time this document or a one of its sub-documents was focused.  If
-  // focus has never occurred then mLastFocusTime.IsNull() will be true.
-  mozilla::TimeStamp mLastFocusTime;
-
   // True if BIDI is enabled.
   bool mBidiEnabled : 1;
   // True if a MathML element has ever been owned by this document.