This is the user style version of my Greasemonkey/Tampermonkey user script. They both accomplish the same thing.

More details and screenshots here:
https://greasyfork.org/en/scripts/1529-metafilter-hedgehog-comment-pointer

Version 4.0 (* note: this is actually the first public release of the user style. The versioning starts at 4.0, to match the version of the user script on which it's based)

As of 2016-08-21: Tested to be working in Firefox and Chrome. Should work for all official MeFi themes (Modern, Modern Dark, Classic, Plain).

If you're using this with the Classic or Plain themes *and* have Plutor's metafilter_scroll_tag script enabled: Edit the z-index in the user style to a negative value ("-10;") to display the Scroll Tag marker above the hedgehog layer.

Credits

* The hedgehog image is licensed by Depositphotos.com/(c) artjazz:
http://depositphotos.com/3438006/stock-photo-Hedgehog-isolated-on-white.html

* This particular hedgehog was suggested by jessamyn:
http://metatalk.metafilter.com/21102/hooray-for-readability#936714