How can you control window focus in Firefox?

I'm trying to open a pop-up window but keep the opener window in focus. This is pretty easy in everything except Firefox.

This will suffice for most browsers:

window.open('gets-opened.html', '', 'width=600,height=400,status=0,scrollbars=1,toolbar=1,menubar=1,resizable=1,location=1');

window.focus();

In Firefox, the opened window maintains focus. I realize that there is a setting for Firefox to allow JavaScript to "raise or lower" windows and that this is disabled by default.

I have seen sites that are able to get around this, though. Kayak is one example. When you select other providers to compare against from their search, the new windows go behind the main window, even with "raise or lower" windows disabled.

How are they getting around this? I realize that this is a security measure to prevent annoying pop-unders, but it seems odd that, from a pop-up window opened on the same domain, I can change the HTML in the opener window through JavaScript, but not give it focus.