How does one support hierarchical calling between frames and firefox?

When this problem occurs,
I have a page of main.html with many frameworks, such as a.html, B .html, c.html, d.html, and e.html...
These subpages contain a MenuButtonClass () method with the same name as javascript.
In one of the Child pages, I will handle other frames.

Window. parent. frames (x). MenuButtonClass ();

This code has no problem in IE, but it is wrong in firefox!

Later, I wrote the example parent.doc ument. getElementsByTagName ("frame") [x]. MenuButtonClass ();

But still error. Why? I adjusted and found
Extends extends parent.doc ument. getElementsByTagName ("frame") [x] is an object
Isn't there anything else to write?

I finally found the cause today. There were only a few contentWindow attributes.
The example should be written as follows: Upload parent.doc ument. getElementsByTagName ("frame") [x]. contentWindow. MenuButtonClass ();

In this way, it is no problem to support IE and firefox.
Attached sample code
Window example. rar