Those are the only correct pronouns when someone's gender is unknown.
Serious question: What's wrong with their/them etc.? It took me some time to internalize these (very dissimilar to my native language) and they sound perfectly gender neutral to me.
Groups of people have invented and used gender neutral pronouns long before their/them became mainstream. So most likely these are the words that the author have used for many years, and they don't want to change.
A lot of languages don’t have gendered pronouns. They/them is grammatically correct.
We both know there's about a 100% chance that whoever reads gnu.org and writes a browser extension to block JavaScript on a specific site is a male, so "he/him" is better in this case.
We all know that the chance is not 100%. Maybe it's 90%, maybe it's 99.9999%, it doesn't matter: It isn't 100% so he and him are plain wrong.
I do think neopronouns are silly when used like this but silly is better than wrong.