While I was online, my internet connection was light and green in the System Preferences > Network and at the top of the address bar, I clicked on the App Store. It took long time to load and then displayed the message, "Cannot connect to the App Store".
I then visited mozilla and clicked on the news. Safari displayed a window with this message, "Safari can't verify the identity of the website "blog.mozilla.org. The certificate for this website is invalid. You might be connecting to a website that is pretending to be "blog.mozilla.org", which could put your confidential information at risk. Would you like to connect to the website anyway?
Then there were 3 buttons to "Show Certificate", "Cancel" and "Continue".
I closed it and clicked on the Firefox link. Safari displayed the error age with the message that read "Safari can't open the page". Then, I read also, " Safari can't open "https://www.mozilla.org/firefox because Safari can't establish a secure connection to the server "www.mozilla.org".
I clicked the back arrow and then on clicked to watch the video with the installation instructions. The page opened and I watched the video.