While not exactly what you've asked, check out uBlacklist add-on. It adds "Block this site" link next to search results in Google, Bing, and a couple of others.

While not exactly what you've asked, check out uBlacklist add-on. It adds "Block this site" link next to search results in Google, Bing, and a couple of others. You can block a specific url and it this add-on will remove it from the search results page.