У вашего броузера проблема в совместимости с HTML5
In order to Merge vertices, you must first Combine multiple meshes.
Merging is for components like Vertex points, Edges, and Faces.
Combining is for objects like polygon meshes and other geometry.
hit 4 to see Wireframe view (helps to see what vertices you have selected)
hit 5 to see Shaded view
To Combine
select two or more meshes
Mesh-Combine
To Merge Vertex Points
select two or more vertex points
Edit Mesh-Merge
sometimes you may have to increase the Distance Threshold if selected vertices are too far apart from each other to Merge