Make Firefox your default
But before you can launch Firefox on Modern, you’ll need to run the Desktop version of Nightly and set it as your default web browser. Also make sure it’s the go-to application for loading HTML and accessing the FTP, HTTP and HTTPS protocols. This is because Microsoft made Windows 8 so that only one browser can be used under the Modern UI. After these are set, you can then go to the Start menu and click the Nightly tile to launch Firefox on Modern.