Here is a firefox add-on that I would like to recommend, it is called Curiyo, i do believe it also works with other browsers Chrome for instance.
http://curiyo.com/
One only has to point at a word and keep mouse button depressed for a couple of seconds until the Curiyo window appears.
This will give you all the information that you may need about the selected word or phrase, it also contains the provision of Wikipedia, Dictionary, Tweets, Images, News, etc.
Try it I don't think you will be disappointed, I wasn't.