Until version 1.2 of the Export to HTML5 plug-in, the levels drop down list was active only in virtual visit mode on purpose.
It's not the case in the version 1.3 that was released tonight. This new version supports also rotation of objects around an horizontal axis, and other new features proposed in Sweet Home 3D 5.5.

Note that this plug-in is less useful now since it's possible to view a sh3d file directly with Sweet Home 3D JS Viewer. Both viewers use the same JavaScript code available in SweetHome3DJS project. The additional processing performed by the Export to HTML5 plug-in reduces the home data handled by the viewer by removing plan icons and reducing the textures larger than 256x256 pixels.

For those interested, I also updated Export to XML/OBJ plug-in to version 1.3.