@Atrion
and
@DEFAULTDNB
System Software Mode allows you to boot into XMB, with additional/more technical information on the bottom-right corner of the screen (haven't looked into that in more detail though).
Release Mode allows you to boot into XMB as well, like a standard CEX console.
Debugger Mode, however, can only allow you to boot up your PS3 with debugging information on-screen, and you cannot start up or access the XMB via conventional means - the only way you can do that is by pressing the PS button, but with that said, you can only access the XMB in an in-game manner, and in order to quit out of
Debugger Mode, switch off your PS3, and then press and hold down the Power button on your PS3 until you hear two beeps in total - one whilst immediately pressing the button, and one whilst holding it down after a few seconds, like how you would do for the Video Resolution Reset.