As of September 8th, 2021, accepted answers are no longer pinned on Stack Overflow and probably soon on other sites in the network as well. For some users, this is the realization of a long-standing request; other users might prefer the old situation. For them, I wrote this simple user script which pins the accepted answer at the top.
That is, if it's on the same page (some questions have so many answers they need to be paginated) and self-answers are not pinned (unless they rank highest in votes/oldest/active, as before).
developed & tested with Violentmonkey on Firefox