I beg pardon in advance if this is the wrong place to ask about tools, but I wasn't sure which other StackExchange site would be appropriate.
I'm training some colleagues on HTML and basic CSS / jQuery selectors, and I feel it'd be very helpful for them to have an interactive DOM tree visualization - something with a broader, clearer view than the inspectors built into Firefox and Chrome.
Years ago there was a Firefox extension called Arboreal that looks perfect, but it's long-since defunct. Does anyone know of a similar tool, ideally one that's interactive and built into the browser? Any browser is fine.