This likely depends on Firefox's user agent. If you have installed the desktop by default extension you should uninstall that, https://addons.mozilla.org/en-US/android/addon/desktop-by-default/ If you don't have that extension install then would you install the Phony extension and try the various user agents listed? We suspect that MetroPCS is lumping Firefox for Android with desktop Firefox. Setting the user agent to one of the Chrome values or iOS values should allow Firefox to use the MetroPCS network. Please let us know if that works around the issue. https://addons.mozilla.org/en-US/android/addon/phony/ Unfortunately if MetroPCS is blocking all Firefox user agents this is something that MetroPCS will need to fix. We can try to contact them but feedback from their customers can be more effective.