When you highlight text, chances are you want to do something with that text. That's the idea behind Auto Context, a free Firefox add-on. The biggest downside to this app is that it doesn't work in more applications.
Once you install the add-on to your Firefox browser, it goes to work. Whenever you highlight any text on a Web page, Auto Context automatically displays a pop-up menu that offers easy access to some of the tasks you're most likely to need. You can, for example, copy the text (as plain text, HTML, real HTML), print it, open it as a URL, save it to a file, search for the term in Google, or search for the term at various Web sites, like eBay and Wikipedia.
And that's not all. You can customize Auto Context to your liking. You can set it to search your preferred search engine, or to search additional sources, such as Google Maps or BabelZilla Glossary. You also can set it so that the pop-up menu doesn't automatically appear. In addition, you can decide whether or not Auto Context will work with editable text.
Auto Context does not work with any text that's part of a hyperlink, which is too bad. But beyond that, its biggest weakness is that you can't use it in more applications. A version is available for the Thunderbird e-mail client, but beyond that it's for Firefox only. I think its features would be even handier in applications like Microsoft Word.
Note: This link takes you to the vendor's site, where you can automatically install the file into your Firefox browser.