You're having this problem on your Windows 7 PC? One possible reason is privacy software that is blocking your user agent information. Could you check this test page and see whether you get the anticipated information at the top and also in the frame?

http://dev.jeffersonscher.com/jstest.html

By the anticipated information, I mean something that includes "Windows NT 6.1".

this is what I get under the "navigator object properties":

navigator.userAgent = Mozilla/5.0 (Windows NT 6.1; WOW64; rv:19.0) Gecko/20100101 Firefox/19.0 navigator.appName = Netscape navigator.appCodeName = Mozilla navigator.appVersion = 5.0 (Windows) navigator.platform = Win32

I'm using Windows 7

Yes, NT 6.1 is Win 7.

Did you get the same in the frame? http://dev.jeffersonscher.com/svrvars.asp

Clear the cache and the cookies from sites that cause problems.

"Clear the Cache":

• Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > Cookies: "Show Cookies"

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Try to boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that helps.