>>/11412/
>  pop up
What do you mean?

In threads there's no embed image and such, only in board view. So I assume you're talking about that.
There should be a figure element which adds a div and an a, which contains the stuff you wanna make disappear. After this figure comes the actual content of the post (divMessage) which holds the link and the Embed button.
I think you could try targeting that figure element, or it's children element with various selectors. No?