--- a/toolkit/components/typeaheadfind/nsITypeAheadFind.idl
+++ b/toolkit/components/typeaheadfind/nsITypeAheadFind.idl
@@ -52,19 +52,22 @@ interface nsITypeAheadFind : nsISupports
    * the selection. */
   void setSelectionModeAndRepaint(in short toggle);
 
   /* Collapse the "found match" selection to its start.  Because not all
    * matches are owned by the same selection controller, this doesn't
    * necessarily happen automatically. */
   void collapseSelection();
 
-  /* Check if a range is visible */
+  /* Check if a range is visible using heuristics */
   boolean isRangeVisible(in nsIDOMRange aRange, in boolean aMustBeInViewPort);
 
+  /* Check if a range is actually rendered (out of viewport always false) */
+  boolean isRangeRendered(in nsIDOMRange aRange);
+
   /******************************* Attributes ******************************/
 
   readonly attribute AString searchString;
                                         // Most recent search string
   attribute boolean caseSensitive;      // Searches are case sensitive
   attribute boolean entireWord;         // Search for whole words only
   readonly attribute nsIDOMElement foundLink;
                                         // Most recent elem found, if a link

--- a/toolkit/components/typeaheadfind/nsTypeAheadFind.cpp
+++ b/toolkit/components/typeaheadfind/nsTypeAheadFind.cpp
@@ -1313,16 +1313,96 @@ nsTypeAheadFind::IsRangeVisible(nsIPresS
       (*aFirstVisibleRange)->SetStart(firstVisibleNode, startFrameOffset);
       (*aFirstVisibleRange)->SetEnd(firstVisibleNode, endFrameOffset);
     }
   }
 
   return false;
 }
 
+NS_IMETHODIMP
+nsTypeAheadFind::IsRangeRendered(nsIDOMRange *aRange,
+                                bool *aResult)
+{
+  // Jump through hoops to extract the docShell from the range.
+  nsCOMPtr<nsIDOMNode> node;
+  aRange->GetStartContainer(getter_AddRefs(node));
+  nsCOMPtr<nsIDOMDocument> document;
+  node->GetOwnerDocument(getter_AddRefs(document));
+  nsCOMPtr<mozIDOMWindowProxy> window;
+  document->GetDefaultView(getter_AddRefs(window));
+  nsCOMPtr<nsIWebNavigation> navNav (do_GetInterface(window));
+  nsCOMPtr<nsIDocShell> docShell (do_GetInterface(navNav));
+
+  // Set up the arguments needed to check if a range is visible.
+  nsCOMPtr<nsIPresShell> presShell (docShell->GetPresShell());
+  RefPtr<nsPresContext> presContext = presShell->GetPresContext();
+  *aResult = IsRangeRendered(presShell, presContext, aRange);
+  return NS_OK;
+}
+
+bool
+nsTypeAheadFind::IsRangeRendered(nsIPresShell *aPresShell,
+                                 nsPresContext *aPresContext,
+                                 nsIDOMRange *aRange)
+{
+  NS_ASSERTION(aPresShell && aPresContext && aRange,
+               "params are invalid");
+
+  nsCOMPtr<nsIDOMNode> node;
+  aRange->GetCommonAncestorContainer(getter_AddRefs(node));
+
+  nsCOMPtr<nsIContent> content(do_QueryInterface(node));
+  if (!content) {
+    return false;
+  }
+
+  nsIFrame *frame = content->GetPrimaryFrame();
+  if (!frame) {
+    return false;  // No frame! Not visible then.
+  }
+
+  if (!frame->StyleVisibility()->IsVisible()) {
+    return false;
+  }
+
+  // Having a primary frame doesn't mean that the range is visible inside the
+  // viewport. Do a hit-test to determine that quickly and properly.
+  AutoTArray<nsIFrame*,8> frames;
+  nsIFrame *rootFrame = aPresShell->GetRootFrame();
+  RefPtr<nsRange> range = static_cast<nsRange*>(aRange);
+  RefPtr<mozilla::dom::DOMRectList> rects = range->GetClientRects(true, true);
+  for (uint32_t i = 0; i < rects->Length(); ++i) {
+    RefPtr<mozilla::dom::DOMRect> rect = rects->Item(i);
+    nsRect r(nsPresContext::CSSPixelsToAppUnits((float)rect->X()),
+             nsPresContext::CSSPixelsToAppUnits((float)rect->Y()),
+             nsPresContext::CSSPixelsToAppUnits((float)rect->Width()),
+             nsPresContext::CSSPixelsToAppUnits((float)rect->Height()));
+    // Append visible frames to frames array.
+    nsLayoutUtils::GetFramesForArea(rootFrame, r, frames,
+      nsLayoutUtils::IGNORE_PAINT_SUPPRESSION |
+      nsLayoutUtils::IGNORE_ROOT_SCROLL_FRAME |
+      nsLayoutUtils::ONLY_VISIBLE);
+
+    // See if any of the frames contain the content. If they do, then the range
+    // is visible. We search for the content rather than the original frame,
+    // because nsTextContinuation frames might be returned instead of the
+    // original frame.
+    for (const auto &f: frames) {
+      if (f->GetContent() == content) {
+        return true;
+      }
+    }
+
+    frames.ClearAndRetainStorage();
+  }
+
+  return false;
+}
+
 already_AddRefed<nsIPresShell>
 nsTypeAheadFind::GetPresShell()
 {
   if (!mPresShell)
     return nullptr;
 
   nsCOMPtr<nsIPresShell> shell = do_QueryReferent(mPresShell);
   if (shell) {

--- a/toolkit/components/typeaheadfind/nsTypeAheadFind.h
+++ b/toolkit/components/typeaheadfind/nsTypeAheadFind.h
@@ -55,16 +55,18 @@ protected:
   void GetSelection(nsIPresShell *aPresShell, nsISelectionController **aSelCon,
                     nsISelection **aDomSel);
   // *aNewRange may not be collapsed.  If you want to collapse it in a
   // particular way, you need to do it yourself.
   bool IsRangeVisible(nsIPresShell *aPresShell, nsPresContext *aPresContext,
                         nsIDOMRange *aRange, bool aMustBeVisible,
                         bool aGetTopVisibleLeaf, nsIDOMRange **aNewRange,
                         bool *aUsesIndependentSelection);
+  bool IsRangeRendered(nsIPresShell *aPresShell, nsPresContext *aPresContext,
+                          nsIDOMRange *aRange);
   nsresult FindItNow(nsIPresShell *aPresShell, bool aIsLinksOnly,
                      bool aIsFirstVisiblePreferred, bool aFindPrev,
                      uint16_t* aResult);
   nsresult GetSearchContainers(nsISupports *aContainer,
                                nsISelectionController *aSelectionController,
                                bool aIsFirstVisiblePreferred,
                                bool aFindPrev, nsIPresShell **aPresShell,
                                nsPresContext **aPresContext);