[ICA-HM620] After upgraded firmware, why can’t see the picture for MJPEG video format via web browser?

That’s because the system with the newer video formats, and the PC need to install the newer DC Viewer software to decode and display the video on PC properly.
Please go to "Control Panel -> Add or Remove Programs" to remove old DC Viewer software at first. Then connect to IP camera via web browser and it will prompt to install the new DC Viewer software in to PC.