English Popup Dictionary is a free extension for Firefox designed to enhance your browsing experience by providing instant definitions of English words. This tool is particularly useful for users who frequently encounter unfamiliar vocabulary while reading articles or engaging in online discussions. The extension allows users to simply hover over a word to see its definition pop up, making it a seamless addition to any web activity.

The extension is categorized under Social & Communication, specifically within social networking, which indicates its utility in facilitating better communication through improved language comprehension. Its user-friendly interface ensures that users can easily access definitions without disrupting their workflow. By integrating this tool into your Firefox browser, you can enhance your understanding of English in a convenient and efficient manner.