A method for a XML editor includes loading one or more files, extracting elements that extend a browser user interface from the one or more files, and presenting a graphical user interface (GUI) for editing the plug-in XML manifest file. The method further includes receiving one or more user edits to the plug-in XML manifest file through the GUI, validating the one or more user edits against properties of the elements, and generating a warning in the GUI for a user edit that conflicts with a property of an element. The method also includes generating or updating XML code in the plug-in XML manifest file in response to the one or more user edits, and saving the XML code.