Oddly, this script doesn't work in chrome. Not sure why not, since it works perfectly in Firefox. If I am reading the code correctly, hiding the parent div of div id="gatewayCreative" seems as if it should work.
The notes on Chrome/Firefox differences that I found here: http://www.chromium.org/developers/design-docum...
Perhaps it's something with the difference in when "injection" occurs? Something that could be fixed using @run-at ( http://wiki.greasespot.net/Talk:Metadata_Block), which chrome now supports? (http://blog.chromium.org/2011/07/chrome-extensi...)