Why does SeaMonkey 2.53 say "rv:60.0"?

[Pim]

Just curious. This throws off the numbering scheme used in the past, where the SM version was "2." plus the Gecko version minus 3. So what happened? Is this actually SM 2.57 in disguise?

I don't have the source here I can look at, but the list of about:config features does look more like Firefox 56 than Firefox 60, tbh.

[therube]

Oh, I believe it's something like...

sites complain when you use a "too old" browser,
so while 2.53 is not "60", 60 could be enough to get you past problematic websites

and while 2.53 is "56", it also includes backports or other parts of later FF versions,
so it is not 56 "exclusively"