gTranslate is a firefox add-on that offers super-simple translation, from Google Translate. It offers translation from any of the 25 languages available with Google Translate. All you have to do is to select some text (which you want to translate and right click, go to "Translate". No more copy paste.
gTranslate makes use of Google translate API and sends the selected text to google translate. Google translate sends back the translated text. All this happens in a blink of an eye. You can choose the language pair by going to the "Change language" option.
When you click on the translated text, a new tab (or window, depending on your Firefox preferences) opens up with Google translate page so that we can see all the translated text.