Are you talking about "Edit Page" in the File
menu? If you are wanting to get rid of flash in a page you are viewing, I don't think that is what "Edit Page" is for. Or are you talking about an extension. If its a FireFox extension, it might not work in SeaMonkey.
If you are wanting to stop Flash in the pages you view, I have two suggestions. One is prefbar
which is billed as "a web proxy with advanced filtering capabilities for protecting privacy, modifying web page data, managing cookies, controlling access, and removing ads, banners, pop-ups and other obnoxious Internet junk." This works as a local proxy your browser sends all requests throught. One of its options is a filter to "Kill embedded Shockwave Flash objects."
Hope this helps.
EDIT: While privoxy can do many useful things, it can also initially take some time to understand and setup (unless you just use the defaults). If you really want to understand its capabilities, you might want to allow an hour or two for this. Prefbar is much more straight forward.