No. The equivalent to firmware was in ROM in later models, but the OS was loaded from disk.

It was unusually complete firmware, comparable to the Mac Toolbox, but you could not use the computer in any way without an OS that had to be soft-loaded.

The Archimedes was a full multitasking GUI OS, in ROM. No disk of any form needed. It could join a network and load apps and save files to a server with no local storage media even installed in the workstation.

This is why Oracle used it as the basis for the original network computer:

https://en.wikipedia.org/wiki/Acorn_Network_Computer

The Pace company, better known for modems and set-top boxes, ended up owning a fork of RISC OS for this purpose. That fork is what led to the current fully-32-bit version and then, later, to the FOSS release.

The Amiga 1000 (that came before the 500) didn't have the "kickstart" in ROM, so you needed a kickstart disk for the 1000.

The Amiga 500 and later had the kickstart in ROM and many of us would mod our Amiga 500 so that we could use a switch to select between kickstart 1.2 or 1.3.

But even on the Amiga 500, that still wasn't a UI from ROM: you had to use the "workbench" disk to get the UI.