Once Bug 1568880 lands, this should fix inspector selector searching over a top-level document and its sub-frames, as part of the fission work. The findNextNode inspector command currently fetches all search results (as a node list) of each of the inspector fronts even though only one node is returned to the front-end on each call. There is a potential for perf issues if there lots of results.

We should investigate (get a profile and some perf numbers) and see the possibility of not having to fetch the whole result set each time.