What matters is not when Windows XP was originally released, but when its official support ended, which according to Wikipedia was on April 2014. Both Firefox and Thunderbird supported Windows XP for a few more years after that (since Windows XP was and is still popular even after its official support ended); version 52 of both (which is an ESR release) is going to be the last one with support for Windows XP.
The operating system support doesn't change within a major release, which is why 52.7 has the same operating system support as 52.0.
> What matters is not when Windows XP was originally released, but when its official support ended
Well, or when a serious replacement arose (because XP was aging at that point). Vista was quite alright if you had a beefy computer, but for the majority I guess it took until 7, which would be July 2009.
Not saying you're wrong or that support should be dropped, I'm just not sure end of support is the best date to use.
I think end of support is a pretty good metric. If Microsoft won’t keep the underlying platform safe, one could argue it’s ethically problematic but to continue to encourage people to use it.
The operating system support doesn't change within a major release, which is why 52.7 has the same operating system support as 52.0.