First I used XPather, then it was FireFinder, and since neither of those seems particularly compatible with the most recent versions of Firefox…
I now use FirePath.
FirePath operates as a Firebug extension and provides a handy “Inspect in FirePath” context menu entry.
FirePath handles XPath, CSS and JQuery selectors.
I don’t have any spare tools extensions in my tool box, so if Firepath dies I’m not sure what I’ll do.
Does anyone have any suggestions to add in the comments?