I guess I have to be one of the last ones to figure this out but  you can get VS.NET to open up Firefox by default and even when in debug mode.  With Firebug installed, running a debug site in FF just makes working on the styles/layouts so much easier.  Now I don't have to attach to process, etc..

You can set this up in two different ways.

1.  File -> Browse With... -> Click Add
2.  Browse With... menu should be on your context menu when you right-click an ASPX page in your solution window.

For me, Browse With... wasn't in my file menu so I had to go to Tools -> Customize -> File and drag it to the file menu.

Giddy Up!