MyPal is a fork of an extremely old version of Mozilla Firefox.
The official GitHub page for the project indicates that it’s been abandoned for one reason or another (although it looks like a new version based off of Quantum is (or was) in development).
https://github.com/Feodor2/Mypal
As a result, I agree with everybody else in this topic. You’re going to have to use a newer operating system or switch web browsers. Very few web browsers support Windows XP nowadays, but Basilisk is an option.
Supporting outdated web browsers and unsupported operating systems that very few people use nowadays is (understandably) not a priority for Discourse.