Röntgen
John Allsopp and the fine folks at Westciv have released a really neat bookmarklet called XRAY. Drag it to your toolbar, visit any website and click on the bookmarklet to reveal a hovering DOM inspector. Clicking on any element in the currently loaded document will reveal not just its position in the DOM tree but also all the styles being applied to it.
Now I now what you’re going to say: You can do this already in Firebug!
Yes, you can but Firebug is a browser-specific plugin. XRAY will work on any Mozilla-based browser or Safari (though it doesn’t yet work in Internet Explorer).
Much as I love tools like Firebug and YSlow, I always feel uneasy about being locked into a specific browser—regardless of whether that browser comes from the Microsoft Death Star or the Mozilla Rebel Alliance. That seem uneasiness also stops me from getting too excited about Greasemonkey scripts. They’re great but I wish that the same functionality was available to all browsers.
Anyway, that’s why I like bookmarklets (sorry Tantek, I can’t really get behind the term “favelet”). XRAY is particularly lovely example of the craft. For another lovely examplar, be sure to grab the microformats bookmarklet from fellow Brightonian Remy Sharp.