Today's hidden gem is a little extraordinary: it is not about a browser technique and it is only available in Firefox with installed Firebug extension. But I expect my target audience having a Firefox as butter and bread tool (thanks for this phrase, Thomas ;-)) fully loaded with extensions and custom settings...

The gem is a search able list which contains all JavaScript files used in the current document. This is perfect if you need to set or modify breakpoints or just want to get a quick overview about the used scripts in the page. If you are dealing with a large amount of JavaScript files, this list is absolutely useless and it gets worse if you are dealing with long paths. And here comes the search able feature in the play: just start typing in the open list and only matching file names are shown.

JavaScript files used in current document
JavaScript files names containing "queue"