In Firefox, press Ctrl+K and — ta da! — your cursor will jump up to the search box in the upper right. Type in a search term (such as “TiVo”) and press Enter. The search results will be displayed in the current browser window, using your default search engine.
If you want to change the search engine by choosing a different one from the pulldown list built in to Firefox, you can press Alt+Down Arrow when your cursor is in the search box, and you’ll see the pulldown menu. Use the Up or Down Arrow keys until the search engine you want is highlighted, then press Enter.
(Note that this feature is for finding web pages. If you just want to search for text on the current web page, you want to Find instead.)