Hide ARCHived WhatsApp (messages count) for FireFox is a utility extension.
It simply hides the annoying indicator for how many archived messages there are.
Just something I needed/wanted.
It's pretty simple and barebones, you could probably do something better.
All it does is look at the classname for the unread chat counter which I know is unique.
It then just gets it by classname, and makes display: none pretty standard stuff actually.