As before, drag on the canvas to rotate the scene, scroll on it to change focal point (perspective projection). Double click it to pause/resume.
I now added Fullscreen mode so that we can scroll on the canvas without scrolling the whole page and use single-key hotkeys without worrying about conflicts with the editor.
    Now, you can select a sphere by clicking on it (literally, click the sphere on the canvas!). And drag it around to move it.
    When a sphere is selected, you can also scroll whe mouse wheel to change its radius, and in fullscreen mode, press B and F key to send it backward or forward according to your view point!
    I also optimized the code a little bit, so that the transformation matrix is completely computed in CPU, and applied (multiplied) inside the vertex shader.
    I suggest moving spheres when pausing the scene by double clicking the canvas, otherwise the spheres are already moving.
    If you found the scene somehow clipped, it seems to be a bug of chromium, please simply click on 'Super Sampling' button or refresh the page. Otherwise the interactions won't work because the coordinates are wrong.