To do what with? Upload? That's totally not the same thing as providing access for directly manipulating the file. That's basically HTML1.0 type stuff. JS file system access to provide a file to, I'm assuming, a WASM app is not even the same sport to be in the same ballpark.

Access for directly manipulating the file isn't necessary (perhaps if the files were enormous, but images and Gerber files aren't). One can upload/download files from a local web app just fine on firefox, and the WASM app can act on the file in memory with whatever APIs it wants.

> in memory

This, but it can also have the browser store it to disk by requesting the persistent mode from the storage API.

https://developer.mozilla.org/en-US/docs/Web/API/Storage_API

You are wrong. You can upload a file to a local web page for example, see this offline only image editing tool I made: https://lelandbatey.github.io/scrapbook_img_print_layout/