One click to quickly know the various English word definitions, IPA, pronunciation with audio – all in a pretty white popup at the top right of the browser, without affecting your browsing experience.
Here is a little more about the One Click Popup Dictionary from the developers:
As you read the web, looking up English words every now and then in a separate website or window can slow you down. In here, you can search the selected word’s definitions super quick in just one click ( or even without a click if you use the shortcut key, Shift +D ) The addon has been configured to look up the word only when you click the button or use the shortcut key, thus avoiding the annoying popups that could otherwise show up on every double click.
Want to get it? You can pick up the One Click Popup Dictionary from the Firefox Add-ons website.