In the main menu of the FMCB configurator you will find the following entry:
Changing that entry to "FASTBOOT: OFF" will inhibit disc booting as the primary boot method that has higher priority than all others (except manual button commands) when it is active.
You might also want to go inside the OSDSYS options menu, and there change the setting "Skip Disc Boot: OFF" to "Skip Disc Boot: ON". With these settings, FMCB will NEVER automatically launch a disc, but will stay in the GUI until you explicitly launch a disc yourself (via Browser or uLE or other homebrews).
I use those settings myself, but also combine them with setting the E1 launch key "Auto:" to the uLaunchELF "BOOT/BOOT.ELF" file, as I always want to boot straight into uLE, regardless of the disc tray contents if any. Then I use uLE to launch anything else I need, including booting of discs when needed.
With the settings I described you can eliminate steps 1-3 here, and leave the disc in the tray all the time. FMCB will ignore it and boot straight into uLE anyway, and there you can then use a shortcut button for PS2rd. (Or any other programs you want to start from uLE.)So the only way I can get PS2rd working is if I boot up the PS2 without a disc in the drive then insert disc whilst in ulaunch.elf. I don't know whether this is intended by the developer or not, but for me the only way that works is:
1. Switch on Free Mcboot modded slim PS2 without a disc in disc tray.
2. Run ulaunch.elf
3. Whilst in ulaunch.elf open lid and insert disc (you will hear it begin spinning)
4. Run PS2rd.elf (which I have in the BOOT folder of my memory card)
5. The black start screen of PS2rd.elf will now show. It will say initializing for about a second then more writing will come up with start game/enable cheats etc.
Best regards: dlanor