https://addons.mozilla.org/en-US/firefox/addon/7675I love this add-on
WikiLook is a Wikipedia & Dictionary look up. Fast, light, open source tool that define words for you without need to open new tabs or extra windows.
Place the mouse cursor within any word, and:
Ctrl + RightMouseButton click = Wkipedia pop-up
Shift + RightMouseButton click = Wiktionary pop-up
Alt + RightMouseButton click = Uncyclopedia pop-up
More then 70+ different languages supported!