From https://forum.palemoon.org/viewtopic.php?f=1&t=13702 :
We will no longer provide updates for Windows XP beyond version 26.5.0 of Pale Moon.
With version 27 just around the corner, we ask that all Windows XP users switch off automatic update checking in Pale Moon to avoid potential problems with incompatible updates. To do this, go to (Tools->)Options -> Advanced -> Update, and select "Never check for updates":