Cookies enabled but actually disabled

I have cookies enabled in my browser settings, but cookies are not functioning - in for example, trying to remain logged into websites (like Yahoo mail).

I usually run Firefox, but have noted that this problem exists no matter what browser I use. I will describe details on Firefox.

Firefox setting: In Tools->Options->Privacy, checked Accept cookies from sites and Accept third-party cookies, Keep until they Expire.

I've always remained logged into Yahoo mail and other sites and could even shut down my computer and reboot - remained logged in. Now that doesn't work. Right now, I'm testing my computer to see if it will work for a "virtual show": (http://robovirtualevents.com/) and it tests cookies, among other things. Their check says cookies are disabled.

Possible hints: I did something extra to clear the cache just before this problem appeared. I don't remember the details and it may have involved removing cookies (which I would have assumed would come back when I clicked to remain logged in again). I clear history when exiting and I also have my browser set to clear everything in the cache when it closes.

Solution 1:

Some "internet security" suites such as McAfee or Norton have cookie-blocking modules built in to them and can as a result of some fault or update end up blocking all sites instead of specific ones.

Check whatever firewall or antivirus suite you are using to see if they are blocking cookies getting through to your browsers.