You can do this by changing two hidden preferences to make View page Source open in an external HTML editor that you can choose. # 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 change it to the path for the HTML editor that you want to use You can also do this by using the Dafizilla ViewSourceWith add-on - https://addons.mozilla.org/firefox/addon/dafizilla-viewsourcewith/ Now in the View menu if you select Page Source, or right-click on a page and select View Page Source it will open in the HTML editor that you selected