> Just might not be able to save...

Oops, I did not read that before going ham in the editor. It seems that the files are stored inside the emscripten file system, so they are not lost. I could download my exported 'test.stl' with the following JavaScript code:

    var data = FS.readFile('test.stl');
    var blob = new Blob([data], { type: 'application/octet-stream' });
    var a = document.createElement('a');
    a.href = URL.createObjectURL(blob);
    a.download = 'test.stl';
    a.click();