AdBlock Plus shows a "Block" button on top of any Flash animation when you hover one. I use some legit (non-adverisement) Flash files in one of my project and I don't like to see any "Block" button there. Here is a short JavaScript code which prevents it from showing up:

$('a[href$=.swf]').remove();

It means: remove all links pointing to location ending with ".swf". This is because Adblock Plus creates such links.

Tested with Adblock Plus 1.1.1 and JQuery 1.3.2.