In Firefox, the search box has a little pull down menu to allow you to choose which search engine it uses. Several popular search engines come included, but not Wikipedia. However, Firefox provides a page on their website listing more search engines you can add to that menu, including Wikipedia's search. To add Wikipedia, simply go here and click on Wikipedia in the list provided, and you are done. To activate it, pull-down the menu at the search box and click on Wikipedia there. Now you have a second Wikipedia search box. Unlike the search box in Wikipedia's sidebar, which disappears off the screen when you scroll down to read a long page, the Firefox search box always remains on the screen, ready to assist. (Keep in mind, typing Alt+F also places the cursor in the Wikipedia search box.)