When working on a web-site I open several windows or tabs and even browsers.
This way I can easily make changes in my post or page without leaving the editor mode and just updating a corresponding visual page (public or private) and saves me valuable time waiting for the page to reload and I can easily make changes in the window/tab where I have the post/page editor whilst I can toggle back and forth updating and easily see the visual difference. Caution – make sure you just have ONE page/post editor open for a specific page/post.
As browsers and screens are behaving differently sometimes just with small but noticeable differences you might even want to have the specific page open in another browser and/or different device and updating as you go to see how your changes display on just that device or browser.
If you have any questions please do not hesitate to contact me directly on email@example.com.