ESM is the new standard with import/export etc. We don't use it now because there are some old mapbox dependencies that only export .cjs, but nothing more than we can handle. Also, firefox has for 5 years struggled to support this in web workers, and now it's about time to move on:

Firefox (Update: Resolved from v114)

Web worker support ships with Firefox 114 PR, Release notes

The issue was around lack ESM support for web workers: https://caniuse.com/mdn-api_worker_worker_ecmascript_modules
5+ years of ongoing effort: https://bugzilla.mozilla.org/show_bug.cgi?id=1247687

Benchmarks

I once attempted to move the benchmark to ESM #964 , but found the change wasn't backward compatible with the already uploaded benchmarks of prev versions, so it was rolled back #969 .

Point of this issue

This can be a tracking issue where we first map the dependencies we have that aren't compatible, and then keep this updated when they are updated