I found a great article on RWW about how to use Drag & DropZones Firefox add-on to extend the Firefox built-in search. After following the steps below, all you have to do is select a word, then drag it using you left mouse button and the Drag & DropZones will overlay on the website you're currently on, and you can drop that word intro a search engine area in the Drag & DropZones to search it on that search engine. You can also add custom search engines. But first, take a look at the screenshot and the little video below, to understand better:
If you would like to use that, first you will need to install Drag & DropZones, then Add To Search Bar so you can add custom search engines, such as Twitter Search. Once installed, restart Firefox and add the search engines you want to your search toolbar. Then go to Tools > Drag & DropZones Settings and you'll see the option to place the search engine links wherever you like on the page, as well as some additional functionality and options. You can of course add some other commands to the DropZones, not just search engines.
If you would like to use that, first you will need to install Drag & DropZones, then Add To Search Bar so you can add custom search engines, such as Twitter Search. Once installed, restart Firefox and add the search engines you want to your search toolbar. Then go to Tools > Drag & DropZones Settings and you'll see the option to place the search engine links wherever you like on the page, as well as some additional functionality and options. You can of course add some other commands to the DropZones, not just search engines.
