I just googled a few URLs here, and found the following:
mozgcp.net is the Mozilla Google Cloud Platform, looking at the links it connects to, it looks as if it is accessing settings for Google, then finding some certificates, accessing pictures for the Pocket service and doing some product detection, why, I have no idea.
moz.works is Mozilla's content delivery network, porbably nothing to worry about.
Detectportal is for captive portal detection, so that firefox knows if you need to log in on a captive portal before using the public wifi network you are connected to.
If that's a stationary computer, that's probably not needed, it can be disabled in about:config so it's easier on the firewall
mozgcp.net is the Mozilla Google Cloud Platform, looking at the links it connects to, it looks as if it is accessing settings for Google, then finding some certificates, accessing pictures for the Pocket service and doing some product detection, why, I have no idea.