From the screenshot, it looks like the firmware is successfully uploaded. Depending on your WiFi network and the browser, after clicking on Connecting, it might not respond and may look as if it’s stuck. But what’s important is to watch the LCD screen: if it can connect to your WiFi router, then it will reboot itself (you may need to unplug and re-plug in power because ESP8266 has a well-known bug that triggers a stall if you reboot right after flashing the firmware. Power cycle it will fix the problem).