Fix Firefox issues in scene mode styling.

1. Change the codified size of the SVG to a higher-resolution, this works around Firefox scaling perforing a raster scale rather than vector.
2. Fix background-position usage, which was incorrect but only working in Chrome because of a Chrome bug which scales incorrectly.
3. The added benefit is that percentages in the CSS are also a little more clean-cut.
Cancel running morphs when home button is clicked.