diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index adaf35920e..6d092a53d0 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -2442,6 +2442,16 @@ nsContentUtils::GetCommonAncestor(nsINode* aNode1, nsINode* aNode2)
   });
 }
 
+/* static */
+nsIContent*
+nsContentUtils::GetCommonFlattenedTreeAncestor(nsIContent* aContent1,
+                                               nsIContent* aContent2)
+{
+  return GetCommonAncestorInternal(aContent1, aContent2, [](nsIContent* aContent) {
+    return aContent->GetFlattenedTreeParent();
+  });
+}
+
 // static
 nsINode*
 nsContentUtils::GetCommonAncestorUnderInteractiveContent(nsINode* aNode1,
diff --git a/dom/base/nsContentUtils.h b/dom/base/nsContentUtils.h
index c6e8070576..9c22fa491e 100644
--- a/dom/base/nsContentUtils.h
+++ b/dom/base/nsContentUtils.h
@@ -338,6 +338,13 @@ public:
    */
   static nsINode* GetCommonAncestor(nsINode* aNode1, nsINode* aNode2);
 
+  /**
+   * Returns the common flattened tree ancestor, if any, for two given content
+   * nodes.
+   */
+  static nsIContent* GetCommonFlattenedTreeAncestor(nsIContent* aContent1,
+                                                    nsIContent* aContent2);
+ 
   /**
    * Returns the common ancestor under interactive content, if any.
    * If neither one has interactive content as ancestor, common ancestor will be
diff --git a/dom/events/EventStateManager.cpp b/dom/events/EventStateManager.cpp
index dd753a97f0..371f66af42 100644
--- a/dom/events/EventStateManager.cpp
+++ b/dom/events/EventStateManager.cpp
@@ -4849,48 +4849,13 @@ GetLabelTarget(nsIContent* aPossibleLabel)
   return label->GetLabeledElement();
 }
 
-static nsIContent* FindCommonAncestor(nsIContent *aNode1, nsIContent *aNode2)
+static nsIContent*
+FindCommonAncestor(nsIContent *aNode1, nsIContent *aNode2)
 {
-  // Find closest common ancestor
-  if (aNode1 && aNode2) {
-    // Find the nearest common ancestor by counting the distance to the
-    // root and then walking up again, in pairs.
-    int32_t offset = 0;
-    nsIContent *anc1 = aNode1;
-    for (;;) {
-      ++offset;
-      nsIContent* parent = anc1->GetFlattenedTreeParent();
-      if (!parent)
-        break;
-      anc1 = parent;
-    }
-    nsIContent *anc2 = aNode2;
-    for (;;) {
-      --offset;
-      nsIContent* parent = anc2->GetFlattenedTreeParent();
-      if (!parent)
-        break;
-      anc2 = parent;
-    }
-    if (anc1 == anc2) {
-      anc1 = aNode1;
-      anc2 = aNode2;
-      while (offset > 0) {
-        anc1 = anc1->GetFlattenedTreeParent();
-        --offset;
-      }
-      while (offset < 0) {
-        anc2 = anc2->GetFlattenedTreeParent();
-        ++offset;
-      }
-      while (anc1 != anc2) {
-        anc1 = anc1->GetFlattenedTreeParent();
-        anc2 = anc2->GetFlattenedTreeParent();
-      }
-      return anc1;
-    }
+  if (!aNode1 || !aNode2) {
+    return nullptr;
   }
-  return nullptr;
+  return nsContentUtils::GetCommonFlattenedTreeAncestor(aNode1, aNode2);
 }
 
 /* static */