Found a neat add-on for FireFox that integrates HTML Tidy directly into FireFox. A yellow warning triangle or green checkbox appears in your status bar to let you know how valid the current HTML page is. Clicking on the status bar icon brings up a source code viewer with questionable lines highlighted, and details on the problems in a three-pane view. Another option will generate the Tidy-cleaned page for you. An added benefit is that the code never leaves your machine, handy when you’re dealing with sensitive data or are off the grid. Neat stuff. Mozilla’s secure add-on site is located here.