Jorge Martinez de Salinas

Dictionary Tooltip is a Firefox Addon that displays on-the-fly word translations in a small tooltip on the same page you’re reading.

Working with Dictionary Tooltip is very easy. You just have to double-click on a word and you instantly get the definition for that word (or its translation to another language).

Dictionary Tooltip comes with many dictionaries and has the ability to add new ones. You can download it here. It works with Firefox 3.5.1.