I have had a number of problems similar to these described here over the years. I would do a search for the problem and find out that all sorts of people were having the problem, and I would see all sorts of complicated solutions. Somehow I would get it fixed. Ironically in terms of this discussion, it was always with FireFox. About two months ago I started having serious problems with FireFox. I would type a word and then wait 5-6 seconds for it to show up on the screen. I described the problem to a friend who is a computer guru, and he told me I was gong to have to do all sorts of radical things to the computer, and none of it sounded good.
On a hunch, I switched to Chrome, and not only did the problem go away, but the whole thing is working much faster than it ever did before.