Look up "UEFI shell" for your vendor. Sometimes this is an unlisted F key, sometimes its as simple as selecting it as which OS you want to boot, sometimes it will happen automatically if no boot device is discovered, sometimes you must supply it as a bootx64.efi from the vendor (or from Tianocore).
Just because UEFI is a standard doesn't mean all the vendors don't smoke crack.
That's only a shell/repl, implementing a DSL for boot-related stuff. It isn't implemented in FORTH, it does not execute or understand FORTH, or use it for anything. It's not there.
It just occupies a similar role in a similar place, of what some FORTHs on some systems once did. Mainly OpenBoot on SUNs and some PPC Apples, while having nothing from their internals.
Having the ability to type some commands in your firmware/BIOS/UEFI, like it has been the case on Sparcs by SUN, PPC Macintosh by Apple, or the OLPC doesn't make it a FORTH.
