I booted to my rarely used XP installation and updated everything I
could. It looks like there will be no more further updates for Chrome or
Firefox.

Chrome went up to version 49 and said no more updates for XP

Firefox, version 44 found no more updates either though it's now up to 45


The virus checker I'm using is Avast, and there were no problems with
that. I was watching the update process and it actually installed a
Microsoft security update which MS is not rolling out for XP users.
KB970158

So...it looks like if one uses Avast, some more mileage can be squeezed
out of XP