Your STM Serial Flasher Web App is really interesting and I get lots of requests from our users to allow our STM32 based product to be updateable via Macs, LINUX, etc.
Our PCBs have a jumper that needs to be fitted to put the device in Boot Loader mode after power up and it would be really great if your Web App had an option not to try and reset the STM32, but to assume that the boot loader is already running.