My site not showing Subscribe RSS button on Firefox, why is that?

Hello!

When I go to my WP blog home page and category pages, I can’t see Firefox “Subscribe to this post” button. Which mean if my blog readers use Firefox, and they click on FF build-in RSS subcribe button, they can’t view my feeds, but I already enable RSS fees and it work fine. What is the issue that Firefox not showing that my site has enable RSS feeds?

My site:

Other sites.

Thanks!