Mozilla hasn’t fully implemented shadow DOM so this is mostly Chrome-specific issue at least for now.
In uBO syntax this can be
:shadow-root() procedural selector which can be used as any other procedural filter. Internally this will be return to old solutions with injected style element or attribute.
Is it already implemented?
The problem is that ad blocking circumvention scripts use
Element.attachShadow and closed shadow roots, which simply cannot be accessed from the outside.
It could be solved by overriding
attachShadow with our own wrapper and keeping track of shadow roots by ourselves. There are ways how they can circumvent our wrapper, though.