In Firefox Desktop, in the developer tools, to highlight an element, we add a <xul:box> on top of the browser and draw another <xul:box> in it. For Firefox Android and Firefox OS, we also want to be able to highlight a node. But drawing a window on top of the content window is not easy (syncing highlighter position when the user scroll or pan is hard). A very easy way to work around that is to use CSS to style the highlighted element. For exemple: "outline:3px solid red". It would be really useful if we could have a dedicated pseudo class. It will be up to the devtools code to add and remove the pseudo class to the highlighted elements, via nsIDOMUtils.addPseudoClassLock().

Comment on attachment 800752 [details] [diff] [review] patch.diff r=me