Yeah, the user might uninstall Firefox, but it's still a very popular and extensible browser. Konqueror has poor compatibility. Most of the pages that I visit look terrible in it. I haven't had much luck with Opera, either. It seems to take forever to load pages. I've tried dozens of browsers and I keep coming back to Firefox. Yeah, it's a little resource-intensive, but it's a small price to pay.
Anyway, I think that the desktop environments that come with PC-BSD should use their browser of choice (Midori, Konqueror, Epiphany.) Firefox could be included on the install disc as an extra. That's how I'd do it, anyway.