Why aren't my previously visited posts highlighted anymore?

[Threehearts]

I can't find a way to make at least the Last visited post highlighted. I really rely on this feature to save time and can only assume that I'm just not working the system correctly.
"Help! I need somebody...".

 

[HorizonsFan]

There is a small envelope to the left of each post. If you have viewed the post, the envelope is closed. If you have not viewed the post, the envelope is opened with a message sticking out.
Not as obvious as the link changing color, but you can tell where you've been.

 

[Threehearts]

As soon as I read your response, I remembered seeing that explanation in the FAQs. Thanks for the reminder1

 

[Coll0610]

The envelope doesn't show as closed until you refresh the page. Just using the back button (like I always do) isn't enough.