The service uses Microsoft's DRM scheme, and as such requires both Windows and Internet explorer. This means that Firefox won't work; take a look at this screen (click for big):

As you can see, Firefox will load the page, but there's no way to actually read the site. Check it out for yourself.
This deal has much more interesting, broader implications on top of one more reason to be annoyed with Wal*Mart. As it stands, they are selling movies for the same price as DVDs, but without giving the consumer the ability to copy the file, burn it to a DVD, or use it at all with other devices. Sad times.
(via theinquirer)
