window.HTMLOptionElement == "[object HTMLElementConstructor]" instead of HTMLOptionElementConstructor I filed this as bug 21842 originally, but that was decided invalid. I'm not sure what the functionality of "new HTMLOptionElement" needs to be, but it seems that window.HTMLOptionElement should be a specifically-named constructor like all the rest of the HTMLElement "subclasses" instead of being just an HTMLElementConstructor. See bug 21842 for more background. To fix this will probably require using a new idl flag "CustomConstructor" to have the JSHTMLOptionElement generated class generate a getConstructor function with the appropriate types.
Created attachment 24682 [details] test case This is a real bug that affects extending HTMLOptionElement prototype, not just a problem with its constructor name.
I have a fix (window.Option and window.HTMLOptionElement are two different constructors, we need to provide both).
Created attachment 24684 [details] proposed fix
Committed revision 37895.