Removed toLowerCase call

This will maybe solve the "InvalidStateError: An attempt was made to use an object that is not, or is no longer, usable" error in firefox.

Numbering was off when dealing with fragments.

It's possible for slides to be in a situation where the last clicked thing was an SVG before the tab/window loses focus. When returning, `.blur()` is called on the previously-active element, but can result in an exception.

This protects against that and will only call `.blur()` when `document.activeElement` supports it.