Cross-domain requests in Firefox

I am developing an OpenSocial gadget (JavaScript language) for RQM (Rational Quality Manager) that gets information from DWA (Doors Web Access). The gadget is running on RQM (https://:<host>:9443/) and I want to make request to the DWA (https://<host>:8443/).
Due to the same-origin policy in Firefox, I get the following error:

> Cross-Origin Request Blocked: The Same Origin Policy disallows reading
> the remote resource at https://<host>:8443/xxxx. (Reason: CORS header
> 'Access-Control-Allow-Origin' missing). <unknown> Cross-Origin Request
> Blocked: The Same Origin Policy disallows reading the remote resource
> at https://<host>:8443/xxxx. (Reason: CORS request failed). <unknown>

As I am using Tomcat I followed the steps described in https://jazz.net/forum/questions/151485/does-rtc-support-cors-cross-origin-resource-needed-for-a-javascript-oslc-consumer to configure CORS but still the same error appears. 

I checked the request/response headers in both Firefox (using RestClient) and Chrome (using Advanced Rest Client Application) but I can´t see "Access-Control-Allow-Origin" response header.  In the case of Chrome, I found an extension named 'Allow-Control-Allow-Origin' and if I enable it, I see Access-Control-Allow-Origin header.

I need to run the gadget in Firefox so, is there an equivalent extension for Firefox? Or how can I avoid using these extensions?

Thanks in advance,