Open Internet Explorer and then press F12 to open the F12 developer tools. On the File menu select File and then Customize Internet Explorer View Source. Here you can select the familiar Default Viewer, Notepad, or Other (which allows you to specify a different program, such as a third-party Web editor).
Once you make this change, whenever you select the View | Source option from the File menu in Internet Explorer, the source code will be displayed in the program you specified.
Tip by Matt Graven, TechNet Tips Editor.