Browser: Firefox 3.6 and IE 8 (no others tested)

I've created a class, Author, and another class that inherits from Author, CoAuthor. In one of my calls to a method of Author against an instance of CoAuthor, I'm receiving an error that seems to boil down to 'this' no long pointing to the object instance, but to the enclosing Window object instead.
All of this code is being executed in a gadget running in an OpenSocial-based framework.
Here are the relevant pieces of code (I think):
Author.js
Code:
1 function Author(name, id, url) {
2     ...
3 }
4 ...
5 Author.prototype.displayAuthorLinkItem = function(resp) {
6 	this.setCoAuthors(resp);
7 	$("#authorList").append(this.getAuthorLinkItem());
8 }
CoAuthor.js
Code:
1 CoAuthor.prototype = new Author;
2 CoAuthor.prototype.constructor = CoAuthor;
3 function CoAuthor(name, id, url, numDocs) {
4     Author.prototype.constructor.call(this, name, id, url);
5     ...
6 }
coauthor-network-profile.js
Code:
1             function processQueryResults(resp) {
2                 ...
3                 authors.sort(Author.prototype.sort);
4                 for(x in authors) {
5                     if(!authors[x] || typeof authors[x] == 'undefined')
6                         continue;
7                     authors[x].getCoAuthors(authors[x].displayAuthorLinkItem);
8                 }
9             }
The getCoAuthors function, called on line 7 in coauthor-network-profile.js, performs an AJAX call and the displayAuthorLinkItem is the callback. When displayAuthorLinkItem is called, I get the following error in Firefox:
this.prototype is undefined
at line 6 in Author.js.
In IE I get:
Object doesn't support this property or method
on the same line.
I've found that if I check the value of 'this' before the call on line 6 in displayAuthorLinkItem, it is an instance of Window, rather than of CoAuthor. I've checked the value of 'this' in calls to other Author and CoAuthor functions and they correctly point to an instance of the surrounding Author or CoAuthor class.

Unfortunately the code is not live anywhere that is publicly accessible. What other information can I provide?

Any assistance is greatly appreciated!