Keep in mind Discourse is very aggressive about deprecating old browser support, as it stands we support: IE11 and up.
In this particular case we would recommend a polyfill for edge and IE. Can I use... Support tables for HTML5, CSS3, etc we have a few other polyfills going now.
Inline scripts are a huge no-no, what we would do is defer load them similar to how Graphviz Plugin does it.
Given the JS requirement here my recommendation here is to start with a very specific discourse-typeform plugin here instead of attempting to bring this in to onebox.