@glyph Loved your #nbpy talk! You mentioned that many libraries on PyPI aren't testing in browser so in case you hadn't seen this yet, urllib3 is being tested in Firefox and Chrome:
https://github.com/urllib3/urllib3/blob/main/.github/workflows/ci.yml#L113
It's definitely not free and the config has been contributed by someone outside of our core team, definitely not straightforward to maintain. Would welcome this becoming much easier for Python projects to do!