Quickly look something up in wikipedia, a dictionary or whatever you like (its easy to add custom sites!). The result is displayed directly on the page.
Whats different from v1.4 ?
There is now a search field incorporated in the result box. There is also tabs, so you can go directly to another search engine. There have been a major cleanup, and a lot of features in 1.4 has been removed (I figured these features obsolete, now that we have the tabs). Also, you should know that you can open the searchbox by clicking SHIFT+CTRL+SPACE

In order to get beautiful search results on the build-in sites, you should also install the LookItUp2 userstyle (This requires the Stylish plugin).

Note: Don't forget to disable the v1.4 script (if you have it installed)

Quick Tour
1. Install the script.
2. Try it out, by clicking SHIFT+CTRL+SPACE
3. The search box will open
4. Enter some text in the search field (Tip: If you select some text before clicking SHIFT+CTRL+SPACE, then the search field will be display this text).
5. Click on the "w" button (also called tab), in order to look it up in Wikipedia
6. Click the ">" button to look it up in the next tab (Which is Wictionary)
7. As default, the system preloads the next tab, so the Wictionary search result should display quickly. Now, while you read the Wictionary results, the next tab (Chambers) is preloading in the background.
8. Click on the page, or press Esc key to close the box
9. Select some text, and press "w".
10. Wikipedia will open in the right side of the page. All sites have shortcuts, so you can go quickly to a specific search engine.
11. While the text is still highlighted, press "i", and a google image search will show up
12. Customize the script by pressing '#' while some text is hightlighted. You can disable the preload feature by changing "cache ahead" to "0", and clicking "Save". I recommend keeping the value low. I think "1" is the best setting, but "2" may be good for you.

Its easy to add sites. Make a search for on your favourite search engine. Copy the url, but replace your word with the string: [words]. You can read more about adding sites on the v1.4 page

Note: Its possible to add cleanup instructions in the url, in order to get beautiful search results (css, xpath selecting, regexp and more). Its all documented on the CleanItUp page (note: use "lookitup" in the url instead of "cleanitup")

Note: This version is still kind of beta. There is probably a bug or two. Please let me know if you see one.
Note: This script does not work in IE7Pro. Fortunately, someone has made a version of LookItUp that works in IE7Pro. Its available here

Install this script

Requirements: Firefox 1.5v or above with Greesmonkey enabled