Tried the Addon store. Firefox's recommended addon has only text translate feature
To Google Translate by Juan Escobar
Right-click on a section of text and click on Translate icon next to it to translate or listen it to your language.
But there is on addon which offers to translate the whole page and also supports Bing Translate
Google Translate, ImTranslator, Dictionary, TTS by Smart Link Corporation
COMPLETELY REDESIGNED TRANSLATOR FOR FIREFOX
ImTranslator translates text, words, webpages between more than 100 languages.
NEW: Inline Translator, Dictionary, access to Google Translate, Microsoft Translator. Unique on the fly localization.
Add to Firefox
This is not monitored for security through Mozilla's Recommended Extensions program. Make sure you trust it before installing.
But is not supported by Firefox. I hate to use plugins which has no recommendation on my browser. Feels a bit insecure.