--- a/toolkit/modules/FinderHighlighter.jsm
+++ b/toolkit/modules/FinderHighlighter.jsm
@@ -579,17 +579,17 @@ FinderHighlighter.prototype = {
     }
 
     // If we're in a frame, update the position of the rect (top/ left).
     let currWin = window;
     while (currWin != window.top) {
       // Since the frame is an element inside a parent window, we'd like to
       // learn its position relative to it.
       let el = this._getDWU(currWin).containerElement;
-      currWin = window.parent;
+      currWin = currWin.parent;
       dwu = this._getDWU(currWin);
       let parentRect = Rect.fromRect(dwu.getBoundsWithoutFlushing(el));
 
       if (includeScroll) {
         dwu.getScrollXY(false, scrollX, scrollY);
         parentRect.translate(scrollX.value, scrollY.value);
       }