The host name "www.sitename.com" allows you to find the machine you wish to connect to.
"http://" tells the system what sort of connection you wish to make, having identified the machine, and is as essential as the host name. For example, you could type "ftp://" instead.
If you omit "http://" in a web browser, the browser will add it for you when it makes the request, on the assumption that is what most people want to do. But Word requires it - that isn't all that surprising, given that Word is not a web browser that is trying its best to be as user-friendly as possible. Bear in mind that whatever you type in the address bar of the browser is subject to an awful lot of "thinking", as these days, you can type search queries and other things in there. Firefox call it the "Awesome bar" rather than the "Address bar".
Adding "http://" to the address in your browser should not cause a problem - I've never encountered that with Firefox before. It's worth trying another browser to see if the behaviour is isolated to Firefox (it sounds like it will be). Then, it might be a case of playing around in the settings. It would be worth checking your firewall settings for firefox.exe. There's some more pointers here:
https://support.mozilla.org/en-US/kb...r-browsers-can
Fascinating
