Lately I’ve been contemplating switching to Safari, as Firefox still seems to be a memory hog, especially since I tend to leave my desktop on for days at a time. With the improvements to the developer tools in Safari 4, there’s less and less reason for me to hang on to Firefox. Couple that with this bookmarklet suite of design/development tools
I just discovered, and the excuse of having to use Firefox for it’s superior developer tools flies right out the window.
The suite includes a configurable grid overlay, a ruler overlay, a measurement tool to determine distance between two points, and a cursor crosshair tool (I’ve not found how to use this one effectively, but it could be useful for figuring placement when using position: absolute).