I am in this situation. A good chunk of my users are stuck on xp so I am stuck on supporting xp too. There is no way around this for me as the reason my users are stuck on xp is because of hardware. Arg!
In my situation there is not even hardware the customer can upgrade to as the original hardware supplier has left the market. We are all stuck with XP until something catastrophic happens.
Latest versions of Firefox cannot be installed on XP. Though, Chrome still works.