I’m just looking at memory usage in windows10 and avast isn’t that much, but firefox is currently showing 1.19GB it is an absolute hog. But I have 8GB of RAM on this system.

On my winXP Pro SP3 (in my signature information) I have 4GB of RAM and again avast’s processes are relatively small compared to many other processes. Memory also fluctuates depending on what other processes are using it and how much you have. The other thing in XP what Memory are you looking at as there are different memory calculations ?