Disable cross domain web security in Firefox

Question

Almost everywhere you look, people refer to the about:config and the security.fileuri.strict_origin_policy. Sometimes also the network.http.refere.XOriginPolicy.

For me, none of these seem to have any effect.

This comment implies there is no built-in way in Firefox to do this (as of 2/8/14).

From this answer I've known a CORS Everywhere Firefox extension and it works for me. It creates MITM proxy intercepting headers to disable CORS. You can find the extension at addons.mozilla.org or here.

Check out my addon that works with the latest Firefox version, with beautiful UI and support JS regex: https://addons.mozilla.org/en-US/firefox/addon/cross-domain-cors

Update: I just add Chrome extension for this https://chrome.google.com/webstore/detail/cross-domain-cors/mjhpgnbimicffchbodmgfnemoghjakai

The Chrome setting you refer to is to disable the same origin policy.

This was covered in this thread also: Disable firefox same origin policy

about:config -> security.fileuri.strict_origin_policy -> false

Best Firefox Addon to disable CORS as of September 2016: https://github.com/fredericlb/Force-CORS/releases

You can even configure it by Referrers (Website).

I have not been able to find a Firefox option equivalent of --disable-web-security or an addon that does that for me. I really needed it for some testing scenarios where modifying the web server was not possible. What did help was to use Fiddler to auto-modify web responses so that they have the correct headers and CORS is no longer an issue.

The steps are:

1. Open fiddler.

2. If on https go to menu Tools -> Options -> Https and tick the Capture & Decrypt https options

3. Go to menu Rules -> Customize rules. Modify the OnBeforeResponseFunction so that it looks like the following, then save:

    static function OnBeforeResponse(oSession: Session) {
       //....
       oSession.oResponse.headers.Remove("Access-Control-Allow-Origin");
       oSession.oResponse.headers.Add("Access-Control-Allow-Origin", "*");
       //...
    }
   

   This will make every web response to have the Access-Control-Allow-Origin: * header.

4. This still won't work as the OPTIONS preflight will pass through and cause the request to block before our above rule gets the chance to modify the headers. So to fix this, in the fiddler main window, on the right hand side there's an AutoResponder tab. Add a new rule and response: METHOD:OPTIONS https://yoursite.com/ with auto response: *CORSPreflightAllow and tick the boxes: "Enable Rules" and "Unmatched requests passthrough".

See picture below for reference: