In Firefox 120.0 for Windows ARM64, viewing (hamburger menu) > Help > About Firefox shows an about window that reads "120.0 (64-bit)" for version. The About dialog does not appear to allow the user to distinguish between ARM64 and x86_64. I can verify in the Windows 11 task manager that Firefox is running as an ARM64 process, but the About page does not expose this.
Considering that Windows 11 ARM64 will silently emulate x86_64 both Windows 10 and 11 will silently emulate x86_32, and that emulation has a performance and battery penalty, my suggestion is to revise how architecture is presented with version number on the About page to make it easier for users to determine which Firefox they're using.