Hopefully, Comcast will be in a position at some point to support browsers other than Internet Explorer. If a Comcast employee is using Firefox, it speaks volumes.
They now have online help forums
(must be a Comcast High-Speed Internet customer to access) which are in beta, that have forums/threads dedicated to other browsers and operating systems including Linux.
Verizon DSL recently became available in my neighborhood. My neighbor across the street has it, but since this is at the tail end of the DSL service area, I do not believe he is getting full speeds with it.
But I'm very happy with my faster Comcast service. 
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; rv:1.7.3) Gecko/20041001 Firefox/0.10.1
SillyDog701 Moderator
xubuntu 9.10