Dialog looks much better now.

browser/base/content/customizeToolbar.xul

@@ -38,7 +38,7 @@
         onload="buildDialog()"
         ondialogaccept="updateToolbar()"
         xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
-        width="700" height="440">
+        width="700" height="465">
 
 <script type="application/x-javascript" src="chrome://browser/content/customizeToolbar.js"/>
 <script type="application/x-javascript" src="chrome://global/content/nsDragAndDrop.js"/>