I like the Firefox developer tools, but still use Safari as my main browser. This little hack helps in at least one aspect of creating sites …
“The Safari Tidy plugin is a small plugin that lets you validate the webpages you browse for (x)html compliance. The actual validation is done by Tidy. This plugin was modeled after a similar plugin for Firefox, which can be found here.
In the bottom right corner of each browser window you will see the amount of warnings and errors the current page has, along with a small icon.”
One note: Make sure you check for updates to this plugin when you update Safari — the last Mac OS X update broke it until it’s functionality until I updated.