AlreadyReddit
Extension Actions
CRX ID
andckodfhlknfcphjcpioeneaoidlfjf
Description from extension meta
Previously viewed comments are colored gray.
Image from store
Description from store
This extension automatically detects which comments you have already seen and turns them gray. This is useful if you want to quickly catch up on a thread without having to wade through all of the comments you have already read. Better than sorting by "new"!
Source is available to browse at the link.
I have no affiliation with Reddit's parent company, Advance Publications, Inc (API). This extension is not endorsed by API.