Heaps of Language Learning Add-ons for the Firefox Browser
The Firefox web browser from Mozilla is not only a great open source web browser. It's also a fabulous tool for language learners! It would take a long time to list and go through all of the cool things you can do with the addons (extensions of Firefox's core functionality) in the language support section of Firefox Addons. Anyone dealing with learning languages online, translation, researching and/or reading content in foreign languages on the Web is encouraged to check out this amazing repository for Firefox addons for Language support.
There is a lot of them, but it's definitely worth the time to sift through and find the ones that work for you.