diff --git a/content/html/content/src/HTMLFieldSetElement.cpp b/content/html/content/src/HTMLFieldSetElement.cpp
index 7729d820ddc2..f1e954bf5990 100644
--- a/content/html/content/src/HTMLFieldSetElement.cpp
+++ b/content/html/content/src/HTMLFieldSetElement.cpp
@@ -217,12 +217,47 @@ HTMLFieldSetElement::AddElement(nsGenericHTMLFormElement* aElement)
 {
   mDependentElements.AppendElement(aElement);
 
+  // If the element that we are adding aElement is a fieldset, then all the
+  // invalid elements in aElement are also invalid elements of this.
+  HTMLFieldSetElement* fieldSet = FromContent(aElement);
+  if (fieldSet) {
+    if (fieldSet->mInvalidElementsCount > 0) {
+      // The order we call UpdateValidity and adjust mInvalidElementsCount is
+      // important. We need to first call UpdateValidity in case
+      // mInvalidElementsCount was 0 before the call and will be incremented to
+      // 1 and so we need to change state to invalid. After that is done, we
+      // are free to increment mInvalidElementsCount to the correct amount.
+      UpdateValidity(false);
+      mInvalidElementsCount += fieldSet->mInvalidElementsCount - 1;
+    }
+    return;
+  }
+
   // We need to update the validity of the fieldset.
   nsCOMPtr<nsIConstraintValidation> cvElmt = do_QueryObject(aElement);
   if (cvElmt &&
       cvElmt->IsCandidateForConstraintValidation() && !cvElmt->IsValid()) {
     UpdateValidity(false);
   }
+
+#if DEBUG
+  int32_t debugInvalidElementsCount = 0;
+  for (uint32_t i = 0; i < mDependentElements.Length(); i++) {
+    HTMLFieldSetElement* fieldSet = FromContent(mDependentElements[i]);
+    if (fieldSet) {
+      debugInvalidElementsCount += fieldSet->mInvalidElementsCount;
+      continue;
+    }
+    nsCOMPtr<nsIConstraintValidation>
+      cvElmt = do_QueryObject(mDependentElements[i]);
+    if (cvElmt &&
+        cvElmt->IsCandidateForConstraintValidation() &&
+        !(cvElmt->IsValid())) {
+      debugInvalidElementsCount += 1;
+    }
+  }
+  MOZ_ASSERT(debugInvalidElementsCount == mInvalidElementsCount);
+#endif
 }
 
 void
@@ -230,12 +265,46 @@ HTMLFieldSetElement::RemoveElement(nsGenericHTMLFormElement* aElement)
 {
   mDependentElements.RemoveElement(aElement);
 
+  // If the element that we are removing aElement is a fieldset, then all the
+  // invalid elements in aElement are also removed from this.
+  HTMLFieldSetElement* fieldSet = FromContent(aElement);
+  if (fieldSet) {
+    if (fieldSet->mInvalidElementsCount > 0) {
+      // The order we update mInvalidElementsCount and call UpdateValidity is
+      // important. We need to first decrement mInvalidElementsCount and then
+      // call UpdateValidity, in case mInvalidElementsCount hits 0 in the call
+      // of UpdateValidity and we have to change state to valid.
+      mInvalidElementsCount -= fieldSet->mInvalidElementsCount - 1;
+      UpdateValidity(true);
+    }
+    return;
+  }
+
   // We need to update the validity of the fieldset.
   nsCOMPtr<nsIConstraintValidation> cvElmt = do_QueryObject(aElement);
   if (cvElmt &&
       cvElmt->IsCandidateForConstraintValidation() && !cvElmt->IsValid()) {
     UpdateValidity(true);
   }
+
+#if DEBUG
+  int32_t debugInvalidElementsCount = 0;
+  for (uint32_t i = 0; i < mDependentElements.Length(); i++) {
+    HTMLFieldSetElement* fieldSet = FromContent(mDependentElements[i]);
+    if (fieldSet) {
+      debugInvalidElementsCount += fieldSet->mInvalidElementsCount;
+      continue;
+    }
+    nsCOMPtr<nsIConstraintValidation>
+      cvElmt = do_QueryObject(mDependentElements[i]);
+    if (cvElmt &&
+        cvElmt->IsCandidateForConstraintValidation() &&
+        !(cvElmt->IsValid())) {
+      debugInvalidElementsCount += 1;
+    }
+  }
+  MOZ_ASSERT(debugInvalidElementsCount == mInvalidElementsCount);
+#endif
 }
 
 void
diff --git a/content/html/content/test/mochitest.ini b/content/html/content/test/mochitest.ini
index e96f458a7464..1c1263f7af1d 100644
--- a/content/html/content/test/mochitest.ini
+++ b/content/html/content/test/mochitest.ini
@@ -398,6 +398,7 @@ support-files =
 [test_mod_attributes_reflection.html]
 [test_mozaudiochannel.html]
 [test_named_options.html]
+[test_nested_invalid_fieldsets.html]
 [test_object_attributes_reflection.html]
 [test_object_plugin_nav.html]
 [test_ol_attributes_reflection.html]
diff --git a/content/html/content/test/test_nested_invalid_fieldsets.html b/content/html/content/test/test_nested_invalid_fieldsets.html
new file mode 100644
index 000000000000..42413baa933a
--- /dev/null
+++ b/content/html/content/test/test_nested_invalid_fieldsets.html
@@ -0,0 +1,47 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=914029
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 914029</title>
+  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 914029 **/
+
+  var innerFieldset = document.createElement("fieldset");
+  var outerFieldset = document.createElement("fieldset");
+  var textarea = document.createElement("textarea");
+  textarea.setAttribute("required", "");
+  innerFieldset.appendChild(textarea);
+  outerFieldset.appendChild(innerFieldset);
+  SpecialPowers.forceGC();
+  ok(true, "This page did not crash - dynamically added nested invalid fieldsets" +
+           " work correctly.");
+  var innerFieldset = document.createElement("fieldset");
+  var outerFieldset = document.createElement("fieldset");
+  var textarea = document.createElement("textarea");
+  var textarea2 = document.createElement("textarea");
+  textarea.setAttribute("required", "");
+  innerFieldset.appendChild(textarea);
+  innerFieldset.appendChild(textarea2);
+  outerFieldset.appendChild(innerFieldset);
+  SpecialPowers.forceGC();
+  ok(true, "This page did not crash - dynamically added nested invalid fieldsets" +
+           " work correctly.");
+
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=914029">Mozilla Bug 914029</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>