For GitHub issue #13.
As of time of writing, Firefox and Safari do not support Declarative Shadow DOM. This component does include a small (4 LoC) polyfill but it is scoped exclusively to elements inside of <is-land>.
Note that if chocolate-web-component.js is not available on page load, any <chocolate-web-component> elements outside of <is-land> will be initialized when the file is loaded. This is better solved by implementing defer-hydration in your component code.
Declarative shadow DOM polyfill is not applied to elements outside of an <is-land>