While you are waiting for a response, I wanted to mention this support article, which you probably already have seen, but just in case: How to stop Firefox from making automatic connections.

The redirector.gvt1.com address might be for Widevine. See: Watch DRM content on Firefox.

Hello jscher2000,

first of all, thank you for you advice and sorry for the delay.

I've read the support article you mentioned, How to stop Firefox from making automatic connections. and that worked for some of the automatic connection but it doesn't work for the connection to http://ciscobinary.openh264.org/openh264-win32-0410d336bb748149a4f560eb6108090f078254b1.zip. How can avoid this connection? I even have this preferences "media.gmp-provider.enabled" to false and "media.gmp.gmpopenh264.provider.enable" to false as well.

I achieved to avoid the connection to redirector.gvt1.com changing a setting in about:config. I changed media.gmp-widevinecdm.enabled to false.

I think OpenH264 is used for WebRTC, so perhaps one of those preferences is relevant.

I thought that too, so I looked for settings in the config that let me change that but I didn't find a thing. I just found settings with the string "webrtc" related with logs or debug settings.

All the settings related with H264 are turning to false.

Oh, I think the relevant preferences have the word peerconnection in the name instead of WebRTC.

Thank you for all your support jscher2000.

I didn't find a setting that let me avoid the connection to openh264.org so we finally decided to let this connection pass throught.

All the other connections, we achieved to avoid them at the end.

Thank you again.