To view source code of any website in your favorite source editor:
You can do this by changing 2 hidden preferences.
- Type about:config into the location bar and press enter.
- Accept the warning message that appears, you will be taken to a list of preferences
- In the filter box type view_source
- Double-click on view_source.editor.external to change its value to true.
- Double-click on view_source.editor.path and set it to C:\Program Files\Notepad++\notepad++.exe (if Notepad++ is stored elsewhere change that to where it is stored or you can choose any editor of your preference)