How to fix Connection is Untrusted Problem
My problem: Nearly any website that I try to visit (including mozilla.org), is blocked with a "This Connection is Untrusted" error. Some sites allow for me to fix it by adding an exception under the "I understand the risks" option, but some, such as google.com, don't. I have the same problem on IE, and I don't have chrome. I thought that it might be a network proxy error, but I've selected "No Proxy" and still had the problem, and I don't have the problem on another laptop connected to the same network.
My stats: I'm running Firefox 42.0, on a Dell Vostro 1720, which is running Windows 7.
Wšykne wótegrona (2)
You should NEVER need to add exceptions for well-run sites. Please stop for a few minutes and investigate what's going on.
When you get connection errors for nearly all secure sites, the problem usually is one of the following:
(1) Error in your system's date, time, or time zone, which throws off certificate validity checks. Sometimes allowing computers to use an internet-based time source can introduce this problem.
(2) Firefox not being set up to work with your security software that intercepts and filters secure connections. Products with this feature include Avast, BitDefender, Bullguard, ESET / nod32, and Kaspersky; AVG LinkScanner / SurfShield can cause this error on search sites.
If you have any of these products: This support article will walk you through checking for this problem: How to troubleshoot security error codes on secure websites.
(3) On Windows 10, Firefox not being set up to work with the parental control software Microsoft Family Safety.
To test by turning it off, see: http://windows.microsoft.com/en-us/wi.../turn-off-microsoft-family-settings)
(4) Malware on your system intercepting secure connections.
If #1-#3 don't seem relevant, you could check the certificates for sites where you added an exception to see whether there is a pattern to the "Issued by" information which points to a specific culprit. Here's how:
"3-bar" menu button (or Tools menu) > Options
In the left column, click Advanced. Then on the right side, click the Certificates mini-tab along the top. Then click the "View Certificates" button.
This should open the Certificate Manager. Click the "Servers" tab. Ignore the ones for "*" and check for any servers you remember adding an exception for. You can select some of those and click View to check the "Issued by" information.
Any pattern?
Hmm, also, your post is marked with Firefox version 42.
An update is available once you can connect: this article describes how to get Firefox 54 using the "About Firefox" dialog on the help menu: Update Firefox to the latest release. If you need legacy plugins other than Flash, you can use the Extended Support Release of Firefox 52. See: Why do Java, Silverlight, Adobe Acrobat and other plugins no longer work?
If something is holding you back from upgrading to Firefox 52/54, please let us know so we can suggest solutions or workarounds. Version 42 is not secure; Mozilla discloses security flaws after each new release.