As soon as you've set up a MassFX simulation, you can test the settings by playing it in the viewports. If problems occur, sometimes it's obvious what's going wrong, but if not you can use the MassFX Visualizer to analyze the simulation in detail.
To start the simulation, click the 
Start Simulation button on the MassFX toolbar. As the simulation runs, it updates in all visible viewports, showing you the
results of the simulation as it progresses.
When the simulation starts, display of physical meshes is disabled. If you want to see these (and more) during simulation, use the MassFX Visualizer.
Enabling the MassFX Visualizer
The MassFXVisualizer provides real-time visual information about the simulation, as it runs, in the viewports. To enable it:
Open the MassFX Tools dialog.
The properties include Collision Meshes, which display physical meshes for every rigid body in the simulation.
