מאת משתמש Firefox‏ 37090c (מפתח) בתאריך פבר' 14, 2008 · קישור קבוע

That's just how it is - plugins like Flash aren't like all the other elements of the web page. In particular, the browser doesn't get notified when the mouse moves over a plugin, meaning that the selection in Element Hiding Helper won't change either.

Not that I see any good reason to use Element Hiding Helper on Flash - you want to block Flash, not hide it. So open blockable items list and look for objects (see Adblock Plus FAQ for details).