I seem to recall somebody getting WatchNow to work with firefox by using a plugin that told the accessed page you were using IE instead...you can also use IETabs for firefox. As of now, the only way to get WatchNow working on a linux machine is to run a VM with Windows in it. Unfortunately, its not the most elegant solution. I'm actually trying to do this with my PS3 at the moment, which is a huge pain, but should be awesome once I get it working
There is also the possibility that WatchNow will work once somebody finishes a Silverlight port for linux, which was announced almost a year ago by Mono, but doesn't seem to have gone anywhere
. Here's hoping something gets done soon.