diff --git a/mozilla/content/shared/public/nsXULAtomList.h b/mozilla/content/shared/public/nsXULAtomList.h
index 25ce756dcc8..86fefc4622c 100644
--- a/mozilla/content/shared/public/nsXULAtomList.h
+++ b/mozilla/content/shared/public/nsXULAtomList.h
@@ -122,6 +122,7 @@ XUL_ATOM(toggled, "toggled")
 XUL_ATOM(grippy, "grippy")
 XUL_ATOM(splitter, "splitter")
 XUL_ATOM(collapse, "collapse")
+XUL_ATOM(collapsed, "collapsed")
 XUL_ATOM(resizebefore, "resizebefore")
 XUL_ATOM(resizeafter, "resizeafter")
 XUL_ATOM(state, "state")
diff --git a/mozilla/layout/xul/content/src/nsXULAtomList.h b/mozilla/layout/xul/content/src/nsXULAtomList.h
index 25ce756dcc8..86fefc4622c 100644
--- a/mozilla/layout/xul/content/src/nsXULAtomList.h
+++ b/mozilla/layout/xul/content/src/nsXULAtomList.h
@@ -122,6 +122,7 @@ XUL_ATOM(toggled, "toggled")
 XUL_ATOM(grippy, "grippy")
 XUL_ATOM(splitter, "splitter")
 XUL_ATOM(collapse, "collapse")
+XUL_ATOM(collapsed, "collapsed")
 XUL_ATOM(resizebefore, "resizebefore")
 XUL_ATOM(resizeafter, "resizeafter")
 XUL_ATOM(state, "state")