diff --git a/dom/xul/nsXULElement.cpp b/dom/xul/nsXULElement.cpp
index 5f9000f69386..f29d2aeebb4e 100644
--- a/dom/xul/nsXULElement.cpp
+++ b/dom/xul/nsXULElement.cpp
@@ -620,27 +620,6 @@ nsXULElement::UpdateEditableState(bool aNotify)
     UpdateState(aNotify);
 }
 
-#ifdef DEBUG
-/**
- * Returns true if the user-agent style sheet rules for this XUL element are
- * in minimal-xul.css instead of xul.css.
- */
-static inline bool XULElementsRulesInMinimalXULSheet(nsAtom* aTag)
-{
-  return // scrollbar parts:
-         aTag == nsGkAtoms::scrollbar ||
-         aTag == nsGkAtoms::scrollbarbutton ||
-         aTag == nsGkAtoms::scrollcorner ||
-         aTag == nsGkAtoms::slider ||
-         aTag == nsGkAtoms::thumb ||
-         // other
-         aTag == nsGkAtoms::datetimebox ||
-         aTag == nsGkAtoms::resizer ||
-         aTag == nsGkAtoms::label ||
-         aTag == nsGkAtoms::videocontrols;
-}
-#endif
-
 class XULInContentErrorReporter : public Runnable
 {
 public:
@@ -697,11 +676,23 @@ nsXULElement::BindToTree(nsIDocument* aDocument,
     // 'scrollbar' that may be created implicitly for their content (those
     // rules being in minimal-xul.css).
     //
-    // This assertion makes sure no other XUL element than the ones in the
-    // minimal XUL sheet is used in the bindings.
-    if (!XULElementsRulesInMinimalXULSheet(NodeInfo()->NameAtom())) {
-      NS_ERROR("Unexpected XUL element in non-XUL doc");
-    }
+    // This assertion makes sure no other XUL element is used in a non-XUL
+    // document.
+    nsAtom* tag = NodeInfo()->NameAtom();
+    MOZ_ASSERT(
+      // scrollbar parts
+      tag == nsGkAtoms::scrollbar ||
+      tag == nsGkAtoms::scrollbarbutton ||
+      tag == nsGkAtoms::scrollcorner ||
+      tag == nsGkAtoms::slider ||
+      tag == nsGkAtoms::thumb ||
+      // other
+      tag == nsGkAtoms::datetimebox ||
+      tag == nsGkAtoms::resizer ||
+      tag == nsGkAtoms::label ||
+      tag == nsGkAtoms::videocontrols,
+      "Unexpected XUL element in non-XUL doc"
+    );
   }
 #endif
 
diff --git a/toolkit/content/minimal-xul.css b/toolkit/content/minimal-xul.css
index 1db405435513..d01b535d8f26 100644
--- a/toolkit/content/minimal-xul.css
+++ b/toolkit/content/minimal-xul.css
@@ -19,7 +19,6 @@
  */
 
 @namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* set default namespace to XUL */
-@namespace html url("http://www.w3.org/1999/xhtml"); /* namespace for HTML elements */
 
 * {
   -moz-user-focus: ignore;
@@ -48,29 +47,6 @@
   visibility: collapse;
 }
 
-/********** label **********/
-
-description {
-  -moz-binding: url("chrome://global/content/bindings/text.xml#text-base");
-}
-
-label {
-  -moz-binding: url("chrome://global/content/bindings/text.xml#text-label");
-}
-
-label.text-link, label[onclick] {
-  -moz-binding: url("chrome://global/content/bindings/text.xml#text-link");
-  -moz-user-focus: normal;
-}
-
-label[control], label.radio-label, label.checkbox-label, label.toolbarbutton-multiline-text {
-  -moz-binding: url("chrome://global/content/bindings/text.xml#label-control");
-}
-
-label html|span.accesskey {
-  text-decoration: underline;
-}
-
 /********** resizer **********/
 
 resizer {
diff --git a/toolkit/content/xul.css b/toolkit/content/xul.css
index fab40fd0d099..292cc63663fb 100644
--- a/toolkit/content/xul.css
+++ b/toolkit/content/xul.css
@@ -98,6 +98,29 @@ vbox {
   -moz-box-orient: vertical;
 }
 
+/********** label **********/
+
+description {
+  -moz-binding: url("chrome://global/content/bindings/text.xml#text-base");
+}
+
+label {
+  -moz-binding: url("chrome://global/content/bindings/text.xml#text-label");
+}
+
+label.text-link, label[onclick] {
+  -moz-binding: url("chrome://global/content/bindings/text.xml#text-link");
+  -moz-user-focus: normal;
+}
+
+label[control], label.radio-label, label.checkbox-label, label.toolbarbutton-multiline-text {
+  -moz-binding: url("chrome://global/content/bindings/text.xml#label-control");
+}
+
+label html|span.accesskey {
+  text-decoration: underline;
+}
+
 /********** button **********/
 
 button {