Just a few notes from some investigations.

The onload event actually belongs to the window object, not the document object; document.onload is an alias for window.onload.

There was this curious comment in jQuery.event.add but d.setInterval==undefined for this case and it may be unrelated anyway:

// For whatever reason, IE has trouble passing the window object
// around, causing it to be cloned in the process
if ( jQuery.browser.msie && element.setInterval != undefined )
	element = window;

I tried a few other methods, each one by itself to prevent interference; one or both were broken on either IE7 or FF2:

var d= document.createElement( "iframe");
// Tried this and d.src = "http://www.yahoo.com" --nope
d.src="";
// Tried appending first to see if it helped --nope
document.body.appendChild(d); 

// FF2: ok; IE7: Never fires
//$(d).bind("load", function(){alert("ok0");});

// IE7 & FF2: Fires before "done"
//$(d).ready(function(){alert("ok1");});

// FF2: unsupported; IE7: ok
//d.attachEvent("onload", function(){alert("ok2");});

// FF2: ok; IE7: Never fires
//d.onload = function(){alert("ok3");};

// FF2: Never fires; IE7: Fires twice, "interactive" "complete"
//d.onreadystatechange = function(){alert("ok4 "+d.readyState)};

// IE7 & FF2: Never fires
//$(d).bind("onreadystatechange", function(){alert("ok5 "+d.readyState)});

// IE7: Never fires; FF2: Permission Denied exception
//$(d).bind("click", function(){alert("ok6");});

alert("done");

That's as far as I could get.

I have noticed, in FF 2.0, that attaching events to new windows that load content from a different domain (for example, http://mysite.com has a link that uses window.open() to load http://www.yahoo.com) is pretty much impossible because of the "same origin policy"(1). Perhaps this is related?

(1) http://www.mozilla.org/projects/security/components/same-origin.html

Related to #939?

With the move to DOM Level 2 event handlers in the latest SVN this is now resolved as much as possible.