Sounds like you have the so called "Google Redirect" virus installed. Instructions on this site on how to remove it: http://www.bleepingcomputer.com/virus-removal/remove-tdss-tdl3-alureon-rootkit-using-tdsskiller

If your system is infected with that virus, then it may prevent you from accessing that site and you may see something else instead. So I've included a screenshot of what you should be seeing when you click the above link.

If you are redirected somewhere else, then you're unlikely to be able to access any security software sites which will enable you to download an app to remove it. In that particular case, use a different computer (one at work, or a friend's) to download the apps you need. Then copy them to a USB Flash Drive. You can copy them from one of those to your own machine.

If this suggestion resolves the problem for you, please click the Solved it button next to this post after you log in into the forum. This will help others searching for a solution to the same problem.

Thanks.

Almost forgot. The "Ask Toolbar" is also known to cause redirects. If you have it installed, remove it by clicking the orange Firefox button, go to Add-ons, then Extensions. Remove it in there.