I have a Mid-2011 iMac that I love and would hate to part with. I put an additional 16gb of memory in it a few years back as well as replacing the HDD with a 1TB SSD. It aged out of Apple support and is currently running High Sierra, 10.13.6. I have free versions of Malwarebytes and Avast Security running on it. If I upgraded to a paid security package and used either Chrome or Firefox, is this computer safe to use? I also have a 13 inch Macbook Pro about the same age running the same OS Version and security packages. Thanks.