It keeps track of how many replies a post has, and shows the number of new replies in red when there are new ones. It marks a post as fully read when you click on it in the list.

It caches the number of replies on closed posts to save bandwidth

It will also show deleted posts, and if you had seen the post before it was deleted it will tell you the title.

PREFETCHER NOTICED ME

Step 1 - Install greasemonkey from the chrome web store here

Step 2 - Click here

Step 3 - Click install on this screen:

Step 4 - Go to https://boards.dangeru.us/lain and make sure it works

To reduce bandwidth as much as possible, the extension will not query threads that are closed if they've been seen before

The algorithm works like this