tabs.open("[url to amo xpi file]") does not work on aurora and nightly

[raymak]

alternatives: use AddonManager to install and addon directly (and silently) -> the user experience is bad a workaround:

exports.installAddonFromAmo = function(url){
function ready(tab){
let worker = tab.attach({
contentScript: 'document.querySelector("a.button.installer").click();'
});
worker.destroy();
tab.off("ready", ready);
}
require('sdk/tabs').open({
url: url,
inBackground: true,
onReady: ready
});
}