Userscripts.org

Try this code or install it from here.

// ==UserScript==
// @name          Flickr Favorite Finder Link
// @description	  This script adds a link to fd's favorite Finder Page page (http://flagrantdisregard.com/flickr/favorites.php). if you visit someones favorites page a link is added to show your photos in this specific collection of favs.
// @author        Nils K. Windisch (netomer)
// @version       0.1 (18/05/06)
// @namespace     http://netomer.de/
// @include       http://flickr.com/photos/*/favorites/*
// @include       http://www.flickr.com/photos/*/favorites/*
// ==/UserScript==

// v0.1 May 18th 2006 initial release
// modified by LouCypher

var extras, header, userId, links, img, link, youLink, you, other;

extras = document.getElementsByClassName('Buddy');
//links = document.getElementsByClassName("Links");
links = document.getElementById("candy_nav_menu_you");
youLink = document.getElementById("candy_nav_button_you");

if (!extras || !links) {
	return;
} else {
	extras = extras[0];
}

other = extras.innerHTML.split('buddyicons/')[1];
other = other.split('.jpg')[0];

you = document.evaluate("./span/a", youLink, null, 9, null).singleNodeValue.href.match(/\w+(?=\/$)/);

link = document.createElement('a');
link.href = 'http://flagrantdisregard.com/flickr/favorites.php?user1='+you+'&user2='+other+'&button=Go';
link.appendChild(document.createTextNode(' Your Photos in these Favs'));
links.appendChild(link);