diff --git a/toolkit/content/widgets/autocomplete.xml b/toolkit/content/widgets/autocomplete.xml
index 83826ee32f43..7774281c8a52 100644
--- a/toolkit/content/widgets/autocomplete.xml
+++ b/toolkit/content/widgets/autocomplete.xml
@@ -975,15 +975,13 @@
       <method name="_invalidate">
         <body>
           <![CDATA[
-          // If we do not have a specific height, we'll have to figure out what
-          // our actual height should be dynamically.
           if (!this.hasAttribute("height")) {
             // collapsed if no matches
             this.richlistbox.collapsed = (this._matchCount == 0);
 
-            // Adjust the height, but we need to delay this because adjustHeight
-            // gets the wrong values (see the comments in _adjustAcItem about
-            // overflow.  XXX why?).
+            // Dynamically update height until richlistbox.rows works (bug 401939)
+            // Adjust the height immediately and after the row contents update
+            this.adjustHeight();
             setTimeout(function(self) self.adjustHeight(), 0, this);
           }
 
