If you keep the 3d viewer open, it will do a live render of the component. So as you scroll up and down the list of footprints you will get a render of each footprint in turn in the 3d window.
Kicad benefits from being used on a big display or even better two displays so that you can see multiple windows at the same time. This is especially useful when you keep the schematic and routing windows open. The 3d render is also live on the current pcbnew layout.
That live render sounds like an awesome feature, John_Pateman. So I decided to try it in kicad 5.0.2 on a PCB that already shows a proper 3D view in pcbnew.
After playing with it for awhile, and determining you meant double-clicking on a component in the right-hand column (NOT the left-hand column) it worked! A very nice feature indeed! Thank you, John. Thank you, developers.
Thanks, I opened the 3d viewer on a second screen and you can do a live render of each component. That will save a a lot of time when browsing through components.