One category not appearing in Firefox?

I'm hoping you can help me with this problem, which has been driving me nuts.

My WordPress site does not display the posts in one of my categories on either of my computers (one Mac, one Windows) in Firefox.

I tried to clear my history and the problem persists. I've asked others to check if it appears for them on their computers, and it does.

What could be wrong with my Firefox?

The site is here: The category that is not appearing is called Advertisements. The top result on this page should be one: