hi, what is the exact address/url of the website where you try downloading from?

www.mcafee.com

would you be able to do a screenshot of that "red fox" and attach it here? (i'm not aware of any security feature in firefox that would look like this)

I can't get to McAfee with any web browser that I have installed. https://www.mcafee.com/

Not a Firefox problem. It's a DNS issue or maybe a DDoS attack on that domain - or maybe they forgot to pay their domain registration fee??

McAfee has been taken over by Intel.

This website is not allowed.

home.mcafee.com

Reason for the lock: This website may harm your computer and your personal information. (Comodo DNS) Fox Web Security expresses its gratitude to the following DNS services which provide more security for the users:

   Yandex.DNS
   OpenDNS
   Norton ConnectSafe
   Comodo DNS

this appears to be caused by the "fox web security" addon then. please look into its options or disable it altogether if it doesn't function correctly.

Disable or remove Add-ons