I read this post on a surface pro with 4GB mem using Firefox. Opened Task Man and no other apps or windows opened was using 41% of mem resources. Opened Libre Office spread sheet and it was only using .1 more so that would not be the issue. I would look to Chrome and any add-ons that might run. Also, like it or not, Cortana is always working in the background and in the top 5 hoggers even if you don't use it.