S3.Translator adds the power of Google Translate’s automatic translations to your browser!
It supports translation of selected text, entered phrase or whole webpage between any of 100+ languages.
• Language learning. Now you can not only translate, but also learn the selected language.
• Automatic translation of subtitles on YouTube.
To enable: Open settings - tab Translate - YouTube Subtitles
• Options: Actions: “Selected text” and “Single word” More Info »
The extension uses Google Translate so it provides more than 80 languages which you can use for quick translation.
Also, the extension able to auto-detect the language of the original text.
There are a lot of simple and complex extensions for Firefox browser but they all have same problem: when translating, the format of selected text is lost, while S3.Translator retains the HTML formatting of web pages.