JavaScript Oddity in FireFox
This is what I thought would work -- it does in IE, and each of the individual lines works on their own in FireFox, but together in FireFox you don't get a popup:
window.open('NewPage.aspx');
document.location = 'PreviousPage.aspx'; // window.location doesn't help, neither does location.href
The following is what turns out to work in both IE and FireFox -- I hope this trivial piece of JavaScript helps someone out there since it took me a few minutes:
window.open('NewPage.aspx');
location.replace('PreviousPage.aspx');