GoPhone APN settings for Firefox OS
GoPhone Internet & MMS APN settings
Open the Settings app in Firefox OS.
Go to Cellular & Data, Turn on Data Connection.
Scroll down and tap Data Settings button and get the screen to enter the APN Settings.
Go to Cellular & Data Message Settings
MMS Proxy: proxy.mobile.att.net
MMS Port: 80
On Firefox OS, APN settings should be entered in correct case. For example, if you are configuring your APN setting with GoPhone Internet & MMS APN settings configuration above, make sure you enter APN as phone and not as PHONE or Phone.