The Problem: “Your connection is not secure” message in Firefox and not able to navigate the web at all.
The OS: Windows 7
Here’s a detailed explanation of what it means, and what you can do: https://support.mozilla.org/en-US/kb/what-does-your-connection-is-not-secure-mean
My issue was that the computer’s date and time was wrong. After fixing the date and time settings in Windows. I relaunched firefox and all was funcitioning well again.
Cool video that I followed: