The”MPH Firmware launcher”allows to launch a firmware from the PSP’s memory stick. The firmware must be in file format and not in eboot.pbp format, for convert a firmware eboot.pbp in file, use the psardump02a tool. Use the tool at own risk! Release notes:

I have just finished the last version of firmware launcher which allows to play video (MPEG4 and AVC) with firmware 2.00 launched (2.50 bug).