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Mozilla Firefox Addons 
dictCheck - Double click on any english word in a page to get the polish meaning. Uses fast online dictionary.
Simple and easy! Enjoy!
Online Hungarian<->English dictionary by SZTAKI based on Jaap A. Haitsma's Dictionary Search 0.4
Modified by Danidek to be installable for Firefox 4.0 and later
The official extension from the people at Dictionary.com, the most popular and trusted online dictionary and thesaurus, to look up word definitions and synonyms anywhere you go with Firefox via a simple pop-up.
Online Hungarian<->English dictionary by SZTAKI based on Jaap A. Haitsma's Dictionary Search 0.4
TEST version
Show, in a new Tab, the meaning of a selected English word with the site Dictionary.com, Thesaurus.com, Reference.com or Reverse Dictionary.
A minimalism English-English Dictionary. Move your mouse pointer over a word and hold CTRL key for a second to see its definition. Possibly, KitaDic is the least obtrusive dictionary extension ever made.
This is an add-on where you can search online easily. Depending on your need you can select your search option. eg: to find a meaning select Dictionary.com and to search use Google.
Provides quick look up of difficult words with audio, phonetics and usages. Just press (Shift + Mouse Right Click) on any word and all the information pops up in the same window.
Look up a selected word in a online English-Japanese dictionary and show it on a pop-up window.
The next generation Rikaichan dictionary catered for translators and Japanese enthusiasts. A fan creation by a single wholehearted translator.
A Korean popup dictionary based on Rikaichan
Requires the additional dictionary addon.
Provides easy inline interface for dictionary service while reading news/articles.
No need to go to separate tab and type keyword to get details, just double click on the word (or right click for link) and details will be displayed on the same page.
