It seems as if Microsoft has abandoned the idea of writing extensions (or plugins, or BHOs, or whatever it's call now) for IE. I can't seem of find any documentation on the topic that's less than 5 or 6 years old. Is this even a thing anymore? I've written one for Chrome that I'd love to duplicate in IE, but it seems hunting down documentation on this is near impossible.
All I really expect to do with the thing is modify the CSS/HTML of a site visited by the user to add a few niceties. This is a cinch in Chrome, but I don't know where to begin in IE.