My computer started messing up yesterday. Whenever I click on a link like youtube or wikipedia, it opens up a new tab in my browser and leads me to a random site. I can still go to youtube and wiki if I type it the searchbar the www. thing. Anyone know what the problem is and if there is any free program that can fix this?

I’m already using avg and spyware terminator. they havent helped any though. Im also using mozilla firefox.