FY18 as in Fiscal Year 2018 ?

Well since WinXP doesn't receive security fixes Firefox is only as safe as WinXP is safe and a lot of other software on WinXP is no longer maintained with (security) updates.

About the only Windows requirements changes for Firefox I have seen for near future is that when Win64 for Release (as early as Fx 38.0) finally comes out it will need 64-bit Windows 7 and 8.x at minimum. The 64-bit XP, Vista and Servers are not supported.

Note that some newer HTML5 media player features may not work in Windows XP like playing MP4 files (no Windows Media Foundation, not sure about Media Source Extensions support).

My experience with Firefox is that Mozilla doesn't make arbitrary decisions about ending "support" for old operating systems - regardless whether those OS's are E-O-L and how long they are E-O-L. I don't recall the details when Mozilla support for Win95 or Win98 / ME ended, but when support for W2K was stopped it had to do with the "engine" (Microsoft Visual C++ Redistributable) that was being used to build Firefox. Mozilla needed to use a newer version of "C++ Redistribute" for the newer versions of Windows; probably Win7. And Microsoft had removed code from the later version of Visual C++ which was particular to W2K or compatibility code in W2K was just missing.

There is a lengthy support thread over at MozillaZine about "updating" W2K to make Firefox 13+ and other programs compatible with the "SP5" a group of coder's came up with. http://forums.mozillazine.org/viewtopic.php?f=37&t=2482475

IMO, "someone" is probably working on extending the life of WinXP far into the future, but right now guessing whether Firefox will be still be "compatible" with WinXP 3 years down the road is silly.

But James mention about "The 64-bit XP, Vista and Servers are not supported." sounds a bit ominous. Plus with all the HTML5 features Mozilla has added to Firefox lately, it may not be worth the effort / time to verify continuing compatibility checks for WinXP (to make sure a new feature works on WinXP). Mozilla has been "trimming the fat" as they are adding the new features.

I still also use XP SP3 and Firefox. Because at my level of usage, security is seldom an issue, and because I am cheap and don't want to invest in a new computer and want to work XP to the bitter end. Anyway, here's a question along the same lines. Not about "security" but rather formatting of webpages. Recently, i have noticed that some pages on the web no longer load into a friendly format- that is to say, things like banner placement is odd, and other images either don't load or load in a strange place on or off the screen. (These same pages load fine and in what appears to be the proper format in Chrome, for example.)

Is this a Firefox thing or a Windows thing going forward? Is there a new set of formatting protocols or coding or something in the Windows 10 Internet world that Windows XP and/or Firefox just will no longer be compatible with?

Specifically, the new DRAFTKINGS.com Lobby.