This guy created a Firefox extension to force the CORS (access-control) headers from a call. This is very useful when you want to do a JavaScript/AJAX query over another website that doesn’t allow the cross domain calls.
His code is on github. I’ve the XPI compiled version on my blog (into a ZIP file) found from jo.se/f website.
You’ll need to add the addon bar (restored) in order to use ForceCORS.
Then you have to go to the about:config and search for forcecors.headers in order to set it up as you need. If it’s for an intranet with credentials required, then check my tip on github.
Make sure you have restarted Firefox and click on the cors that appears into the bottom addon bar of Firefox. It should switch to red. You can now do cross domain calls!