Give your button an id something like this:
<input id="mybutton" type="button" value="Dont show this again! " />
Then use jquery (to make this unobtrusive) and attach click action like so:
$(document).ready(function (){
$('#mybutton').click(function (){
fbLikeDump();
WriteCookie();
});
});
(this part should be in your .js file too)
I should have mentioned that you will need the jquery libraries on your page, so right before your closing body tag add these:
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
<script type="text/javascript" src="http://PATHTOYOURJSFILE"></script>
The reason to add just before body closing tag is for performance of perceived page loading times