If you click on the "X time-unit(s) ago" part of the comment heading in a new window/tab, it will open that comment as its own item where you can then favorite it.
It's a little hidden, I have often wished the same thing as you without remembering that favoriting comments is possible, even though I've evidently done it before since when I favorited the parent I found other favorited comments in my favorites list.
If you ever decide to dip your toes into the hi-fi world, there are a lot of objectivist, engineering-minded audiophiles out there. I would say they outnumber the "magical thinking" audiophiles by a significant degree online. It's been a really fun hobby for me!
If you click on the "X time-unit(s) ago" part of the comment heading in a new window/tab, it will open that comment as its own item where you can then favorite it.
It's a little hidden, I have often wished the same thing as you without remembering that favoriting comments is possible, even though I've evidently done it before since when I favorited the parent I found other favorited comments in my favorites list.