Firefox does not enable cookies when using netConnection (RTMPT)

I have been trying (for several days) to make this work: I want to connect to media servers using the RTMPT netConnection. To achieve this, I have to pass an authentication cookie along with my request. In Chrome and IE it works, but in Firefox it doesn't pass auth_cookie.

When I go through the logs I see a request for / open / 1, but it has no cookie. Againg: In Chrome and IE, it uses cookie. The cookie does not have the HttpOnly flag.

Another weird scenario I ran into is that it doesn't pass the cookie, the ApplicationServer that is authenticating asks me for credentials. If I enter them, it accepts the cookie and works, and any subsequent connections work (firefox passes auth_cookie on request / open / 1); but if I delete all cookies in the browser (via CookieController-> Delete ALL Cookies and DOM Store) the credentials are requested again (no cookie is passed).

Any suggestions? I've searched all over the internet for a solution, but I can't find anything ...