Thanks, I didn't know that. Mozilla should make that more prominent so that users who don't know what RSS/ATOM is could "subscribe to this website" with just a click.
Mozilla used to make that more prominent. Most users didn't care, because they still didn't know what that weird icon meant. That was ultimately the downfall of RSS - the web tech scene never managed to communicate to the average user what RSS was good for, what it did, and how to use it.
The issue isn't "not knowing about RSS/ATOM". You don't need to. The same way e.g. you don't need to know what the octane numbers for gasoline mean. What you do need to know is what it does for you, and that answer has always been "not enough to satisfy the hassle".
(A good chunk of the blame here goes to all the larger, traffic-hungry web sites that only published excerpts via RSS, with a click-through link. It transformed a useful feed into a rather useless list of self-updating bookmarks)
It needs a better name than RSS/Atom. It should sound like English: "Subscribe to this website with <better name>." (same icon)
"Really Simple Syndication" and acronyms cause non-technical people to shut down. It's a foreign language. (Edit: "Atom" would be a good name, because it's plain English, and probably a better format too.)
RSS/Atom didn't decline because of Mozilla -- it declined when Google killed Google reader.
The information overload could be solved with machine learning algorithms (run locally in the client) that sort posts into a "featured" folder.
There are solutions to all of the current issues with RSS/Atom.
That's the problem with RSS/Atom. "Feed reader" doesn't mean anything to most people. "Subscribe to this website" does.