CVE affected range is always far too wide. It obviously can't affect anything before ~75 or so because firefox didn't have the timeline api before then. It's annoying that they don't distinguish an unknown lower bound.
Well, I think their thinking is that:
* we don’t want users to run 75
* 75 is so riddled with CVEs by now, who cares if there is one more
But I agree it’s appears lazy because it would have been easy to determine in that case, if I understood you correctly. Someone would have had to test it though, at the very least.