Yesterday I downloaded the Comodo IceDragon browser which is based upon the highly popular Firefox browser. Comodo claims that it is a more secure and faster browser then Firefox itself.
The browser has a SiteInspector button which allows you to scan the page that you're on for malwares and viruses. You can also check links whether they're malicious or not by right clicking on the links and choosing the "Scan Link With Site Inspector" option.
Well enough of me promoting the security features of IceDragon, below are the tutorials on how to change the default Yahoo! Search into Google Search.
1. Type "about:config" at the browsers address bar. You'll be taken to the warranty page. Click on the button that says "I'll be careful, I promise!".
2. Type "Search" at the search bar and you'll see a list of preference settings. Find a preference name called "keyword.URL".
3. Double click on it and a value box will pop out. change the value into "http://www.google.com/search?&q=".
4. Open a new tab and make a quick search at the address bar. It should show you Google search results if done correctly.