Given your previous posts about how much you have on your hard disc I fear that this could well be your problem.
The more data you have on your disc, the harder it has to work:
If your disk has less than 15% free space, Windows would have a problem defragmenting the disk. When you are using a lot of RAM and little left, chunks of it will be farmed off the the pagefile. This further uses up CPU resources and avast is likely to scan these movements into and out of memory.
When you consider that the actual CPU activity is I would say reasonable, your memory usage is high.
If you have Low RAM resources to start with and low hard disc space this only loads the system further.
I think you really need to do some serious house keeping (that I have mentioned in your other related topics), or get a larger HDD and or Increase RAM.
Firefox can be a bit of a RAM hog when having multiple tabs open (but isn't that RAM is for), on my old XP system periodically I restarted firefox to clear that build up.
See attached mage of my win10 laptop task manager (which is effectively my primary system) and you will see a totally different story, it has 8GB DDR4 memory, 256GB SSD, 1TB HDD drives with plenty of space and a RAM remaining.
