ref: Firefox developer release notes
Firefox Quantum 57 for developers
Firefox 60 for developers
Firefox 59 for developers
Firefox 58 for developers
Firefox 56 for developers
Firefox 55 for developers
Firefox 54 for developers
Firefox 53 for developers
Firefox 52 for developers
Firefox 51 for developers
I was going to edit it but then noticed it is auto-generated.
Oops. Interesting. Thanks for spotting that! I will try to take a look at it.
Sheppy
Actually, someone else probably needs to do that if they can find time. I’m swamped. 
It’s using {ListSubPages()}}, which lists the subpages alphabetically. So, “Firefox Quantum …” comes before any “Firefox N”, where N is a number. I renamed the Fx 57 page to "Firefox 57 (Quantum) for developers, so it appears in proper sequence.
I was about to suggest a different fix to this problem, but I see you’ve already made a change, which fixes it just fine. Thanks Janet!