How to fix Google Redirect Virus

Why am I redirecting to different websites connected with Google? When I search on google.com and clicked on the result pages, I am being redirected to other pages plus a countless pop-ups of websites connected to Google keeps on appearing.
I am using Mozilla Firefox 3.6 as my default web browser and it always brings me to annoying websites that I don't really intend to go. And while I am trying to find a solution on how to fix this error, I constantly have to click the back button because I am being redirected to other pages that are completely not relevant to what I am looking for.
I cleared the cache and everything but that did not resolve my problem. And as I searched on a site, I found out that this is a virus that could not only redirect to different websites but can also compromise my personal data's such as credit card information and many more.
How can I completely remove this from my system without having to use third party application? My computer is acting really slow. It seems like something is blocking my internet and I am always taken to a different fake websites. My system is running Windows 7 Ultimate. Any help will do. Thanks in advance.
