Highlight text while scrolling down in Safari

I have the same problem as this user, Help me highlight text while scrolling down and I really need this to be resolved.

The original post experienced the problem in 2012 and I thought maybe they would have fixed this in 2016 but it still doesn't seem to work properly.

The problem is that I can only highlight my text in safari if I start highlighting the text from the bottom of the page and move my mouse up. It does not work if I start highlighting my text from the top of the page and move my mouse down.

Does anyone know why this is the case?

I do not want to use my keyboard to highlight my text. I just want to use the mouse as it gives me better control over what I want to highlight.

Also I have no extensions installed.

This is as far as the highlighting goes if I try to highlight text starting from the top of the page while moving the mouse to the bottom of the page.