In file, open a new window and then open the page you want into it. You will then have both windows open. I just found that out...lol. I keep one smaller than the other and switch back and forth. I’m old, it’s the only way I’ve found.... :)
I just found out if you keep both windows small, you don’t need to switch back and forth. Both can be viewed simultaneously. I’m a happy camper!
You can make both windows small enough that you can see both of them. Click the middle button on the right hand top of the window and then use the arrows(move the mouse to the edge of the window and you will see a double headed arrow) to size the window. If you can’t see the arrows click the middle button again.