How to identify the browser and redirect the user if that’s not the correct browser?

I have a website to do for university and the teacher wants us to include code that checks what browser the user is using and if the browser isn’t Firefox, they should be redirected elsewhere.

I have this so far:

function fnBrowserDetect(){                            
  let userAgent = navigator.userAgent;          
  let browserName;                    
  if(userAgent.match(/chrome|chromium|crios/i)){              
    browserName = "chrome";            
  }else if(userAgent.match(/firefox|fxios/i)){              
    browserName = "firefox";            
  }  else if(userAgent.match(/safari/i)){
    browserName = "safari";            
  }else if(userAgent.match(/opr//i)){              
    browserName = "opera";            
  } else if(userAgent.match(/edg/i)){              
    browserName = "edge";            
  }else{              
    browserName="No browser detection";            
  }                     
document.querySelector("h1").innerText="You are using "+ browserName +" browser";            
}

function redirect(){
  if(browserName != "firefox"){
    window.location.replace("www.google.com");
  } else {
    window.location.href = "../index.php";
  }
}

Can someone help me out and let me know how can I do this correctly?