WTF?

I've been away for a while. During that time I've upgraded to the latest FireFox and added a few security add ons. Now when I try to sign into the site i get this:

Warning: your browser doesn't send the HTTP_REFERER header to the website.
This can be caused due to your browser, using a proxy server or your firewall.
Please change browser or turn off the use of a proxy
or turn off the 'Deny servers to trace web browsing' in your firewall
and you shouldn't have problems when sending a POST on this website.

I've disabled all the add ons and turned on cookies and it still doesn't work. Internet Explorer works fine, but its a turd. I want FF back. Am I missing a checked box somewhere that is still messing me up? Thanks in advance guys.

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EDIT:

I entered about:config into the address bar and then went through the settings until I found network//http:referral...... and changed the value from 0 to 1 and now all is well.  I don't know what implications that has on the security of the browser or anything but it seems to have solved the immediate problem.