main.js

tabs.open({
    url: src,
    inBackground: true,
    onLoad: function(tab) {
        tab.attach({
            contentScriptFile: self.data.url("print-page.js")
        });
    }
});

print-page.js

alert('yup');

document.addEventListener('pagerender', function(e) {
    alert("test");
}, true, true);