Yeah I remember that. I just searched and see over 2000 TCS posts with “hir” dating back to April 1996 (the month the TCS list started)! So that’s 30 years ago now!
“Hir” was often paired with “s/he” (which is also in over 2000 posts). It was also common to use ungendered nouns like “parent” and “child” instead of “he” or “she” (and “parent’s” and “child’s” were used too).
I used “hir” in my first TCS post in 2002 and in a few dozen other posts (sometimes I only quoted it, so I don’t have an accurate count).
I don’t think “hir” is a good option because when you say it out loud (or in your head to yourself while reading) it sounds like “her”.