Via Ned Batchelder, I found TaskSwitchXP, which is very useful! I often have a zillion windows open, and the normal task switcher is not good enough to distinguish different instances of applications and windows. I’ve tried other similar addons, but this is both fast and very customizable.
Via Tom, I found Jim Andertons blog, which mentions Venkman. It is a JavaScript debugger, that can be used to find those irritating small typos and bugs (not written by me of course ;-). It seems to be a jewel, and I will probably use it when I’m back from vacation!