Facebook address bar no longer says "https://".What should I do?

I checked off "secure browsing" in the settings a month or so ago and the address bar within facebook has said "https://" up until tonight. I haven't been able to add any aps, so that's not the problem. It's still checked off in the settings, but for some reason, "https://" is crossed off in the address bar now. I'd really like some input on what's wrong. Thanks.