Fuente: electron/electron#1344 (comment)
En el main index.html
// index.html
// Open all links in external browser
let shell = require('electron').shell
document.addEventListener('click', function (event) {
if (event.target.tagName === 'A' && event.target.href.startsWith('http')) {
event.preventDefault()
shell.openExternal(event.target.href)
}
})