FeedLock

eedLock helps you stay on top of your Reddit feed. It dims posts you’ve already seen so new items stand out, and it remembers where you stopped reading so when you come back to the same feed, the page can scroll back to roughly that spot. Your read state and scroll position are stored locally in your browser (Chrome extension storage).

How to use it
Install FeedLock from the Chrome Web Store and pin it if you like (optional).
Open Reddit (reddit.com) as usual — the extension runs on Reddit pages automatically.
Reading posts: When you scroll a post into view, click it, or otherwise engage with it, FeedLock can mark it as read and gray it out so you can tell what’s new at a glance.
Unread filter: Use “Unread Only” in the floating panel (bottom-right) to hide posts that are already marked read.
Bulk actions: “Mark All Read” marks every post on the current page as read; “Clear Read” clears your read marks for a fresh start.
Resume reading: When you return to a feed you’ve used before, FeedLock tries to restore your last scroll position and may show a short “Last position” toast so you know it jumped back.
Settings: The panel also reflects options like forcing “New” sort (if you enabled that in the extension) so feeds stay consistent with how you browse.