<NOSCRIPT> elements' rendering is slightly delayed

A user on our blog noted (https://blog.torproject.org/comment/279207#comment-279207) that they get a warning about JavaScript being enabled despite have the security slider set to "Safest".

See: http://dreadditevelidot.onion/post/5c1fcd0539a3a5484eb3 for an example page and some discussion on it.

I tried a bit but so far failed to provide a minimal testcase outside of the .onion space.