On Firefox 146.0.1 for Ubuntu number of all and unread articles are not updated when new articles are fetched. It seems that data for earlier fetched articles is somehow overwritten, items are disappearing.
I've also tweaked the available settings - no help.
I'd join the earlier reviews that maintenance of this addon is lagging behind.
I like the idea to handle my RSS feeds in my web browser, I also like the looks and features of this addon, but now I am switching to another solution.