FireFox won't load certain pages

Problems associated with FireFox 1.5.0.4 that I don't think I had before the upgrade. Both pages shown below successfully load using Microsoft Internet Explorer (ie) . If ie had tabbed pages, I'd be ok using it.

Here are two examples of pages that won't load. It's apparently a random event. Any ideas on getting to the bottom of this issue will be appreciated.

jeff@jeffchapman.com

Example One. Trying to study the Xplane company web site.
Attempted url: http://www.xplane.com
Tab title: "(Untitled)"

Example two. Trying to log into my web mail client from network solutions.
Attempted URL: http://mail.jeffchapman.com
Tab Title: "Network Solutions Webmail"