HTML validation with Safari Tidy
A great extension for Firefox is the HTML Validator extension, which uses Tidy to automatically validate the HTML of every page you open in Firefox. This extension is one of the reasons I have for keeping Firefox running all day alongside Safari, my main browser.
But now, thanks to Kasper Nauwelaerts, you can add the same functionality to Safari. The Safari Tidy plugin works in a similar way to the HTML Validator extension, but it does miss a few features.
When Safari Tidy is installed, the rightmost part of the status bar at the bottom of the browser window will display the status of each page you visit. If a page contains invalid HTML, a warning or error icon will be displayed along with the number of warnings or errors. If you view source, all errors and warnings are shown in a list and will be highlighted in the source.
This is the first release of the Safari Tidy plugin, so maybe more features will be added later. (via Veerle)