Use the Firefox address bar instead of the built-in search box to search any website or search engine.
By default, if you enter a search query in Firefox's address bar, the browser will perform a Google "I'm Feeling Lucky" search. You can change this so it will perform a normal search using Google or any other search engine you want.
Fewer text input areas = simpler & faster searching
It's much more efficient to use a single input field for all text entry, rather than one for addresses and another for search. This eliminates the need to think about which one to use based on what you want to do, which means one less keyboard shortcut to memorize, and one less decision to make.
Computers can do a pretty good job of figuring out what to do based on what you enter, so let the browser work for you, and get in the habit of always using the same keyboard shortcut to jump to the address bar, whether you're navigating or searching. After you try it for a while, you'll wonder why anyone would want two text input areas. No, it's not perfect, but it works great 99% of the time.
One less thing on the toolbar
Now you can free up space on the toolbar by removing Firefox's built-in search box (right-click on the toolbar, select Customize, and drag the search box off the toolbar). If you were using it to access other search engines, try setting up Quick Searches for those instead. Quick Searches use the address bar, and let you quickly perform a search on any website or search engine.
Make a quick change to your user.js file, then restart Firefox
Edit your "user.js" file, and add:
// Change to normal Google search:
You can substitute the URL with the appropriate syntax for whatever search engine you want to use.
You may have heard about making changes like this by typing "about:config" in the address bar, but as far as I can tell, those changes apply only to the current browser session, and don't persist when you restart.
Note: You must restart Firefox for this change to take effect.