The window of a VirtualBox VM with EFI boot simply cannot fit my laptop screen - and I hate running a VM with scrollbars. So, after looking around for while, I found the solution. Understandably, it requires running command line.

    VBoxManage setextradata LiveBox VBoxInternal2/EfiGraphicsResolution 800x600

I want the window for my VM (LiveBox) to be at most 800x600. We can check that value by running,

     VBoxManage getextradata LiveBox VBoxInternal2/EfiGraphicsResolution

While we are at it, to view the current firmware used by a VM,

    VBoxManage showvminfo LiveBox | grep Firmware

And, finally, to actually select a firmware (options: bios / efi),

    VBoxManage modifyvm LiveBox --firmware efi

That's about that.