How do i make Safari my main internet browser?

I'm not sure if i'm using the write terminology but let me explain! i have a macbook pro laptop and the internet thingy is originally safari. However, i downloaded firefox in case there was ever a problem with safari. Now whenever people send me links and i click on them the web page opens up in firefox and not safari! How can i make it and what can i do so that when i click on a link in an email or aim safari will open up the web page and not firefox!