After running for a while my pc is slow. SVCHOST.exe taking all the system resources. I close the process and the pc is fine for a while. This has been happening for days. I finally come to find out that it is Firefox because when I close the process all program work fine but Firefox. When I try to close Firefox the pc display a black screen. I have to hold the power buttong to shut down and then reboot the pc. Any ideas why this happens?

PS. I reset FireFox.