ImTranslator Dictionary translates words and displays alternative translations along with the part of speech.
In addition to the translation variants, each dictionary entry displays a set of reverse translations to the original language, if available.
The Dictionary covers over 90 language combinations with English language and many other language pairs.
The dictionary's translations are provided by the Google Translate dictionary.
http://about.imtranslator.net/tutorials/presentations/imtranslator-translator-for-firefox/firefox-imtranslator-dictionary/