"new posts" has disappeared from my Forums tab. Have been using it for years, but it is gone now...
Firefox 52.0
I just noticed: If I click on"forums", I see "new Posts" for about 30ms, and then "new posts" gets overwritten with "Watched Threads ". Is it something I did?
This is my banner now. It used to look like John's:
For those of us for whom it works, there is no ellipsis after "unanswered threads". That implies something is hidden in your header. Try clicking on that. When I mess with it to get the ellipsis (using "inspect") and click on the ellipsis, the drop down shows "New Posts." If that appears, maybe you can pull it back to your header in typical Windows fashion.
Don't know if if this will help if the problem recurs :-
Deleting the ETO cookie removes the "Keep me signed in" function.
"New posts" doesn't appear if you aren't signed in.
If your browser window is narrower in width then the ellipsis appears and some options disappear (you have to click on the ellipsis to see them). If you make your browser window wider all of the options will appear, assuming your zoom isn't set too high.