When position:sticky was the new hotness, Filament Group came out with an excellent polyfill to give the Apple Safari experience to other browsers.
But since that time, sticky has had mixed fortunes. Apple still encourages it and Mozilla adopted it, but since the switch to the blink engine, Google Chrome has dropped it while they focus on squeezing scrolling performance from their render pipeline.
Meanwhile, IE doesn’t look likely to adopt it. With patchy support, you’d think it would die out, but I find more and more reasons to have this sort of behaviour.
Unfortunately the filament group polyfill was built for a specific user case. There’s no support for elements hitting the bottom of a container and sticking there, so more awkward use cases like a sticky sidebar are not possible.