On this thread...
...John TH said that Firefox is not supporting XP after version 55, and thus that is the reason why more recent versions of Firefox Portable won't launch in XP. However, I have the same problem in Cherry Tree: v 0.38.0 works fine, but 0.38.3 won't launch.
This problem might affect a lot more apps than just Firefox and cherry Tree, but those were the only two I updated before finding the problem. Any thoughts, John?
FYI I am on:
Firefox 52.02 to latest
Cherry Tree 0.38.0 to latest