NetworkInformation.downlinkMax - Web APIs
function logconnectiontype() { var connectiontype = 'not supported'; var downlinkmax = 'not supported'; if ('connection' in navigator) { connectiontype = navigator.connection.effectivetype; if ('downlinkmax' in navigator.connection) { downlinkmax = navigator.connection.downlinkmax; } } console.log('current connection type: ' + connectiontype + ' (downlink max: ' + downlinkmax + ')'); } l...
...ogconnectiontype(); navigator.connection.addeventlistener('change', logconnectiontype); specifications specification status comment network information apithe definition of 'downlinkmax' in that specification.

nsIDOMMozNetworkStats
to create an instance, use: var networkstatsmanager = components.classes["@mozilla.org/networkstats;1"] .createinstance(components.interfaces.nsidomnetworkstats); attributes attribute type description connectiontype domstring connection type of the stats.