Update: I'm finally getting the new site with SeaMonkey.

An apparent improvement related to the change to the new website (but not on the website itself): For the first time ever, Avis finally sent me a confirmation email as soon as I made the reservation. I haven't changed my email address at their site for years, but it never sent me one when I made reservations on the old site. But the first reservation I made on the new site, a few minutes ago, it promptly sent me one. ^