Firefox/Safari doesn't support ESM in service workers. This means it throws an exception during parsing.

See: https://caniuse.com/mdn-api_serviceworker_ecmascript_modules

https://wordpress.slack.com/archives/C04EWKGDJ0K/p1701734039961329?thread_ts=1701734039.961329&cid=C04EWKGDJ0K

Creating this issue to track adding a better error.