Follow up to Bug 1053898. See - https://bugzilla.mozilla.org/show_bug.cgi?id=1053898#c147 - https://bugzilla.mozilla.org/show_bug.cgi?id=1053898#c247 We use a non anonymous walker when fetching children of a shadow root to avoid jumping to pseudo elements that are not really children of the shadow root. But consequently we won't read any anonymous child either. That might either be solved by using an anonymous walker with a specific filter. Or by trying to start the walker from the shadow root and then navigating to its chidlren (I believe this prevents it from jumping to children from other nodes, but to be checked again).

From duplicate bug 1483663 (In reply to Tim Guan-tin Chien [:timdream] (please needinfo) from comment #0) > So in the ordinary Shadow DOM world, siblings of a Shadow Root gets ignored, > or "moved" under the <slot> element in the Shadow DOM. That's not the case > for native anonymous content. They continue to be rendered by layout as if > they are in the same place, but with the Shadow Root present, they no longer > show up on the inspector. > > The concrete example would the soon-to-be-landed bug 1431255, when enabled, > results in the following DOM: > > <video controls> > Shadow Root UA Widget Shadow Root > <div class="videocontrols"> videocontrols > .... > <img /> poster image (NAC) > <div class="caption-box" /> captions (NAC) > > PS there won't be any <slot> inside videocontrols. > PS2 I actually don't know their order in the DOM tree because I couldn't see > them in the inspector :), but I assume DOM happens before layout, therefore, > Shadow Root gets attached before NAC. > > Anyway, it would be nice if the inspector reflects how Gecko handles the NAC > elements, even though it might forever be a special case with UA Widgets.

(reopening bug 1483663 as the two bugs are actually different)