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Dictionary Pop-Up by Dictionary.com (Official) 126.96.36.199.1-signed
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.
About this Add-on
Definition Pop-Up Features Include:
• Click on a word while surfing the web to see Dictionary.com’s definition in a small pop-up
• Customize your dictionary popup to your liking - no other dictionary does this
• Choose a specialized definition for science and medical terms – all from definitive sources
• Sign for our popular Word of the Day email to help you boost your vocabulary