After deleting my Pentium !!! MR setups the Pentium!!!/E 650Mhz as Avenger M99 and the Dual Pentium !!!/EB 1000 as Gradinko, I found out that I still could not select my main system as main Mods Rigs setup, which is Blue-Leader the same I could not select Firefox which is my secondary system.
So even if you would add a new setup, the latest added setup will auto reset as main MR system and even changing your Main setup with a different MR setup, this will not work.
Here a video of how this goes to function:
And yes I have mailed the Webmaster about this, I just post it here so if others also have this issue, they too can leave reply and see that they are not the only ones that have this similar problem.