Oracle relased version 5.0 of VirtualBox yesterday. I don’t see any firmware features listed in the press, and I’ve not had a chance to do a code review of the new code yet. It has improved CPU and USB 3.0 support, at minimum.
QEMU is the main platform for running UEFI’s virtual firmware: OVMF. But Xen, KVM, and VirtualBox also support OVMF, to some degree. VirtualBox can also be recompiled with EFI-specific build directives to enable additional UEFI diagnostics.
(In somewhat related news, back in March, Oracle’s Linux distro got Secure Boot support.)