Just "Double click" on any word and inline popup is displayed containing details of selected word using public dictionary services.
Now(v0.3) links are also supported, just right click on any link and context menu will display words from the link to look for.
Additionally select the word manually and right click to look-up the word from context menu.
Now(v0.3) five dictionaries are supported, select your favourite dictionary for look-up.
Kindly take a note that this tool provides just interface, actual dictionary service is provided by public interface of selected dictionary website.
v0.4 added Compact Mode, a very simple definition of word for quick look-up.