Macbook pro keeps slowing down

My Macbook pro had been playing up lately. Looking at the activity monitor the Memory Pressure keeps going to red and slowing the computer down. A Safari Web

Content process keeps opening up and causes it to use up all the RAM, slow down and a few times caused it to crash. The process is https://autotrader.portal.com. How can i stop this from running? Every time it opens up by itself I have to force quit it to stop it slowing up and freezing.