Though this is something of a segway, it can be difficult for users to find an STL file they are looking for, when they may have dozens of them on their computer. The Marlin 3D Printer Tool includes an STL Shell extension to make this easier.
After the tool is installed, navigate to its main folder (usually C:\Program Files (x86)\Marlin3DprinterTool) and run "Marlin3DprinterToolStlConfiguration.exe":
This will open the control panel shown above. All you have to do then is click "Install and Register STL Thumbnail", which will make a thumbnail for every STL