It's not just a Windows thing. Trying to load a wasm-bindgened, webpacked site from disk in Safari gives
[Error] Cross origin requests are only supported for HTTP.
[Error] Fetch API cannot load file:///Users/nemo157/sources/cbor.nemo157.com/dist/048579358ee0369cf25b.module.wasm due to access control checks.
and in Firefox
Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at file:///Users/nemo157/sources/cbor.nemo157.com/dist/048579358ee0369cf25b.module.wasm. (Reason: CORS request not http).