Luckily, you can use the amazing polyfill service polyfill.io, to polyfill the required features for you based on your browser user-agent.
<script src="https://cdn.polyfill.io/v2/polyfill.js?features=es6&flags=gated"></script> <script src="https://unpkg.com/spiritjs/dist/spirit.min.js"></script>
Always test your animations in other browsers to make sure it renders correctly. Checkout the Polyfill.io docs for more info about polyfilling browser features.
Pascal Klau has created a dynamic-polyfill package on npm, which only polyfill missing features to minimize browser requests.
The Web Player uses GSAP as the default animation strategy. GSAP does a great job on cross-browser support and performance, yet it might be possible that certain properties are not supported by and can not be animated on older browsers.
Always test you animations in different browsers.