This web application needs to be opened with a chromium based browser to support WebUSB.
On Windows you need to replace the default FTDI USB driver of the FT232R chip. Otherwise no access is possible with WebUSB.
You can do this by replacing the driver with WinUSB using Zadig. In Zadig select "options -> list all devices", then search for your FTDI FT232R device and press "replace driver".
You can uninstall the device (with driver) in Windows device manager to change back to the original FTDI USB driver.