diff --git a/mozilla/content/html/content/src/nsGenericHTMLElement.cpp b/mozilla/content/html/content/src/nsGenericHTMLElement.cpp
index ad13dbab1e7..63e89690a16 100644
--- a/mozilla/content/html/content/src/nsGenericHTMLElement.cpp
+++ b/mozilla/content/html/content/src/nsGenericHTMLElement.cpp
@@ -111,12 +111,6 @@
 #include "nsLayoutUtils.h"
 #include "nsContentCreatorFunctions.h"
 
-// If this flag is set on an nsGenericHTMLFormElement, that means that we have
-// added ourselves to our mForm.  It's possible to have a non-null mForm, but
-// not have this flag set.  That happens when the form is set via the content
-// sink.
-#define ADDED_TO_FORM (1 << NODE_TYPE_SPECIFIC_BITS_OFFSET)
-
 class nsINodeInfo;
 class nsIDOMNodeList;
 class nsRuleWalker;
@@ -2712,6 +2706,8 @@ nsGenericHTMLFormElement::UnbindFromTree(PRBool aDeep, PRBool aNullParent)
       nsCOMPtr<nsIDOMHTMLFormElement> form = FindForm(mForm);
       if (!form) {
         SetForm(nsnull, PR_TRUE, PR_TRUE);
+      } else {
+        UnsetFlags(MAYBE_ORPHAN_FORM_ELEMENT);
       }
     }
   }
diff --git a/mozilla/content/html/content/src/nsGenericHTMLElement.h b/mozilla/content/html/content/src/nsGenericHTMLElement.h
index 97d0657d4bd..01dc70b9391 100644
--- a/mozilla/content/html/content/src/nsGenericHTMLElement.h
+++ b/mozilla/content/html/content/src/nsGenericHTMLElement.h
@@ -877,6 +877,21 @@ protected:
   nsIForm* mForm;
 };
 
+// If this flag is set on an nsGenericHTMLFormElement, that means that we have
+// added ourselves to our mForm.  It's possible to have a non-null mForm, but
+// not have this flag set.  That happens when the form is set via the content
+// sink.
+#define ADDED_TO_FORM (1 << NODE_TYPE_SPECIFIC_BITS_OFFSET)
+
+// If this flag is set on an nsGenericHTMLFormElement, that means that its form
+// is in the process of being unbound from the tree, and this form element
+// hasn't re-found its form in nsGenericHTMLFormElement::UnbindFromTree yet.
+#define MAYBE_ORPHAN_FORM_ELEMENT (1 << (NODE_TYPE_SPECIFIC_BITS_OFFSET+1))
+
+// NOTE: I don't think it's possible to have the above two flags set at the
+// same time, so if it becomes an issue we can probably merge them into the
+// same bit.  --bz
+
 //----------------------------------------------------------------------
 
 /**
diff --git a/mozilla/content/html/content/src/nsHTMLFormElement.cpp b/mozilla/content/html/content/src/nsHTMLFormElement.cpp
index abd825de9c6..a109a77fc93 100644
--- a/mozilla/content/html/content/src/nsHTMLFormElement.cpp
+++ b/mozilla/content/html/content/src/nsHTMLFormElement.cpp
@@ -711,13 +711,91 @@ nsHTMLFormElement::BindToTree(nsIDocument* aDocument, nsIContent* aParent,
   return rv;
 }
 
+static void
+MarkOrphans(const nsTArray<nsIFormControl*> aArray)
+{
+  PRUint32 length = aArray.Length();
+  for (PRUint32 i = 0; i < length; ++i) {
+    nsCOMPtr<nsINode> node = do_QueryInterface(aArray[i]);
+    NS_ASSERTION(node, "Form control must be nsINode");
+    node->SetFlags(MAYBE_ORPHAN_FORM_ELEMENT);
+  }
+}
+
+static void
+CollectOrphans(nsINode* aRemovalRoot, nsTArray<nsIFormControl*> aArray
+#ifdef DEBUG
+               , nsIDOMHTMLFormElement* aThisForm
+#endif
+               )
+{
+  // Walk backwards so that if we remove elements we can just keep iterating
+  PRUint32 length = aArray.Length();
+  for (PRUint32 i = length; i > 0; --i) {
+    nsIFormControl* control = aArray[i-1];
+    nsCOMPtr<nsINode> node = do_QueryInterface(control);
+    NS_ASSERTION(node, "Form control must be nsINode");
+
+    // Now if MAYBE_ORPHAN_FORM_ELEMENT is not set, that would mean that the
+    // node is in fact a descendant of the form and hence should stay in the
+    // form.  If it _is_ set, then we need to check whether the node is a
+    // descendant of aRemovalRoot.  If it is, we leave it in the form.  See
+    // also the code in nsGenericHTMLFormElement::FindForm.
+#ifdef DEBUG
+    PRBool removed = PR_FALSE;
+#endif
+    if (node->HasFlag(MAYBE_ORPHAN_FORM_ELEMENT)) {
+      node->UnsetFlags(MAYBE_ORPHAN_FORM_ELEMENT);
+      if (!nsContentUtils::ContentIsDescendantOf(node, aRemovalRoot)) {
+        control->SetForm(nsnull, PR_TRUE, PR_TRUE);
+#ifdef DEBUG
+        removed = PR_TRUE;
+#endif
+      }
+    }
+
+#ifdef DEBUG
+    if (!removed) {
+      nsCOMPtr<nsIDOMHTMLFormElement> form;
+      control->GetForm(getter_AddRefs(form));
+      NS_ASSERTION(form == aThisForm, "How did that happen?");
+    }
+#endif /* DEBUG */
+  }
+}
+
 void
 nsHTMLFormElement::UnbindFromTree(PRBool aDeep, PRBool aNullParent)
 {
   nsCOMPtr<nsIHTMLDocument> oldDocument = do_QueryInterface(GetCurrentDoc());
 
+  // Mark all of our controls as maybe being orphans
+  MarkOrphans(mControls->mElements);
+  MarkOrphans(mControls->mNotInElements);
+
   nsGenericHTMLElement::UnbindFromTree(aDeep, aNullParent);
 
+  nsINode* ancestor = this;
+  nsINode* cur;
+  do {
+    cur = ancestor->GetNodeParent();
+    if (!cur) {
+      break;
+    }
+    ancestor = cur;
+  } while (1);
+  
+  CollectOrphans(ancestor, mControls->mElements
+#ifdef DEBUG
+                 , this
+#endif                 
+                 );
+  CollectOrphans(ancestor, mControls->mNotInElements
+#ifdef DEBUG
+                 , this
+#endif                 
+                 );
+
   if (oldDocument) {
     oldDocument->RemovedForm();
   }     
diff --git a/mozilla/content/html/content/test/Makefile.in b/mozilla/content/html/content/test/Makefile.in
index 16740b80c3f..bc0f8bd7b37 100644
--- a/mozilla/content/html/content/test/Makefile.in
+++ b/mozilla/content/html/content/test/Makefile.in
@@ -96,6 +96,7 @@ _TEST_FILES = 	test_bug589.html \
 		test_bug386996.html \
 		test_bug388746.html \
 		test_bug389797.html \
+		test_bug390975.html \
 		test_bug391994.html \
 		test_bug392567.html \
 		test_bug394700.html \
diff --git a/mozilla/content/html/content/test/test_bug390975.html b/mozilla/content/html/content/test/test_bug390975.html
new file mode 100644
index 00000000000..3a8c649c0d1
--- /dev/null
+++ b/mozilla/content/html/content/test/test_bug390975.html
@@ -0,0 +1,62 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=390975
+-->
+<head>
+  <title>Test for Bug 390975</title>
+  <script type="text/javascript" src="/MochiKit/MochiKit.js"></script>
+  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=390975">Mozilla Bug 390975</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+  <table id="table1">
+    <form id="form1">
+      <input>
+      <input>
+     <tr><td>
+       <input>
+       <input>
+       <input>
+     </td></tr>
+    </form>
+  </table>
+
+  <table id="table2">
+    <form id="form2">
+      <input>
+      <input>
+     <tr id="row2"><td>
+       <input>
+       <input>
+       <input>
+     </td></tr>
+    </form>
+  </table>
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+/** Test for Bug 390975 **/
+var form = $("form1");
+is(form.elements.length, 5, "Unexpected elements length");
+
+$("table1").parentNode.removeChild($("table1"));
+is(form.elements.length, 3, "Should have lost control outside table");
+
+form.parentNode.removeChild(form);
+is(form.elements.length, 0, "Should have lost control outside form");
+
+form = $("form2");
+is(form.elements.length, 5, "Unexpected elements length");
+
+$("row2").parentNode.removeChild($("row2"));
+is(form.elements.length, 2, "Should have lost controls inside table row");
+</script>
+</pre>
+</body>
+</html>
+