S3.Google Translator is a free Firefox extension that adds the power of Google Translate’s automatic translations to your Firefox browser! It supports translation of a selected text, of an entered phrase or translates a whole webpage between any of 80+ languages.
In addition the extension is able to auto-detect the language of the source text.
There are a lot of simple and complex extensions for the Firefox browser but they all have the same problem: when translating, the format of the selected text is lost, while S3.Google Translator retains the HTML formatting of the web pages.
Available for: Windows, Mac OS, Linux