Crossdomain settings in Google Chrome
This answer was correct when written, but is longer correct, the switch has been deprecated
Chrome has a command line switch for this:
chrome.exe --disable-web-securityYou can view a full list (as of when it was posted!) of command line options for chrome here.
No. Sorry.
Chrome and Firefox, however do support cross-domain requests via the W3C CORS spec (Cross Origin resource sharing) however the remote host has to enable it. If the remote host supports it explicitly then you don't have to make any changes to your XMLHttpRequest to be able to fetch the content.