I'm currently working on a site which uses a subdomain. The subdomain works fine for everybody, every device and every browser I've ever tried, except for Firefox on my computer. My computer is a dual boot HP Pavilion dv6 with Windows 7 and Ubuntu 12.04. I'm experiencing the same problem with Firefox on both OS's.
When I'm trying to access my site aaa.bbb.com I'm redirected to www.bbb.com. When I'm trying to reach another subdomain under the same domain, e.g. ccc.bbb.com, it works fine. My subdomain aaa.bbb.com works fine in Chrome (both OS's) and IE.
I don't use Firefox Sync and I've tried disabling all plugins and all extensions. It's the same no matter if I'm at home or in school, so it's not the router.
Is Firefox's DNS resolving somehow built into the hardware? Or is there some common DNS cache which is used by both Windows and Ubuntu? Do Firefox sync my DNS cache with some server without me knowing about it? I've setup a local domain for this project, aaa.localhost, on my ubuntu partition but that shouldn't matter on Windows, right?
I have absolutely no idea why this happens but I'd very much like to find out.
An interesting note: I just looked at the HTTP headers with HttpFox, Firebug and Wireshark. HttpFox and Firebug both shows that aaa.bbb.com returns a 302 redirect response (to www.bbb.com), but Wireshark doesn't even show the request to aaa.bbb.com. Wireshark can only see the request for www.bbb.com.