Firefox Sync would work perfectly for most users, without the need to spin up a server or host data on the cloud.

That could keep track of feeds you're subbed to, but the problem is keeping track of which posts you've already read. Once you're having to sync all of that, it might as well be a web app.

Why? Firefox Sync already syncs my browsing history, bookmarks, and tabs frequently enough that it appears to be real time from my perspective. What is different about an RSS feed's "read" log?

In my experience, the history and tabs sync when they feel like it. All my stuff ends up there eventually, but I can't expect that I'll sit down, close Firefox on mobile, and have the tabs and history show up on desktop.

I always read about people going on about synching Desktop and Mobile as this killer feature, and it always puzzled me.

I tried using it for a while to check if it would fundamentally make me feel different, but after a couple of years I saw zero benefit.

What are people using that they really need this for?

This is news stories though. You don't want to read the stories on one machine and have it show up again on another machine.

I suppose it depends on how you consume your feeds: do you look at the latest, like a social media timeline? or read every entry of some blogs, like an inbox? I definitely have some feeds I consume like the latter, and I need that to persist and sync.

Maybe that's the thing - the things I read on my cell phone and the things I read on my computer are fundamentally different. I am surprised that I seem to be in the minority on this, maybe.

Likewise, any information or news delivery product being developed today that doesn't take both mobile and desktop into consideration during planning stages is a product you shouldn't use.

Firefox already does some syncing. If they added rss, it's likely that they'd add it to the syncing (as optional).