Those Russians aren't too imaginative these days, are they? Looks like a slightly reworked MiG-25.
That's because the MiG-31 was a follow-on to the MiG-25. The -31 had a crew of two, and a powerful radar for long-range work. It was slower than the FOXBAT, though, by about half a Mach. IIRC, it also wasn't very maneuverable, but then neither was the FOXBAT (which, if all this weren't confusing enough, is the aircraft that FIREFOX was actually based on.).