Firefox: LangLadder is a smart Firefox extension designed to aid you with your foreign-language studies, teaching you vocabulary and improving your reading skills.
Learning another language is one of those goals everyone puts on their goal list at one point or another, but it's also difficult to tackle after work, your social life and other responsibilities. LangLadder integrates with Firefox to help you improve you foreign language vocabulary and reading skills, saving and defining words you don't know with example sentences and flash card features. While its creator suggests that it's best for intermediate to advanced students, it looks like it could work well for anyone trying to expand their skills with a second language.
LangLadder is a free download for Firefox, requires Jetpack extension.