Clicking anywhere generates JS warnings in Firefox iff a dropdown menu is present

Created by: rossmeissl

To reproduce:

1. Create a page with a dropdown button present.
2. Load the page in Firefox
3. Click anywhere on the page
4. See JS Warning appear in Firebug console

Live example

Here is a page with only a normal button:

http://jsfiddle.net/PSGz6/

Clicking anywhere on this page does not generate JS warnings.

Here is the same page with a dropdown button added:

http://jsfiddle.net/pZT5W/

Clicking anywhere in the "result" window does generate a JS warning:

Empty string passed to getElementById().

Other folks have had this issue (#5223, #4263 (closed)) but the issues did not include live examples.