On the site www.slovari.yandex.ru you can add a search engine for Firefox, IE, Opera. After adding it you can search describing of words via a search box in your favorite browser. But this engine describes through different dictionaries. To translate english / a russian word you should select a option in the right navbar (в словарях ABBYY Lingvo). I think this way is an inconvenient and I have created an opensearch configuratuon for this service. Now I can input an english or a russian word in a search box of Firefox (IE, Opera) and then get a translation of it immediately. If you want add this service you should go to this url http://sinnus.narod.ru/opensearch/opensearch.html and add "Lingvo Yandex" engine in the search box.
Then you can search a translation of english/russian box via a search engine.
p.s. For examine a config file you can download it from this url http://sinnus.narod.ru/opensearch/opensearch.xml if you want to change a translation language.