This connection is untrusted with Error code: sec_error_unknown_issuer.

Question

Hello,
When I try to open G-Mail & twitter and some other trusted websites, I got the following warning "This Connection is Untrusted" with Error code: sec_error_unknown_issuer.
For most of the site, I can bypass by clicking « I understand the risk » but this is a bummer but for Gmail and Twitter, there is no other button than "Get me out of here"
When I go through « about:support » and « reinitialise » system, I no longer have the problem, but not only it erases all my personnal set-up but the problem always come back when I restart my system
Date and time are set right.
I have also tried to reinstall completely FIREFOX to no avail
I am using McAfee Total protection 2014 & Firefox 31.0 on Windows 7 64 bits.
I have had this problem for the last 5 days and only Firefox.
Other Browser ( IE8.0) is working fine
I have searched for solutions but they all failed -
Deleting cert8.db did not solve the problem either
How do I solve this Problem?
Thanks and Regards

Answer 1

You can check the connection settings.
*Tools > Options > Advanced > Network : Connection > Settings
*https://support.mozilla.org/kb/Options+window+-+Advanced+panel
If you do not need to use a proxy to connect to internet then try to select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly.
See "Firefox connection settings":
*https://support.mozilla.org/kb/Firefox+cannot+load+websites+but+other+programs+can
Do a malware check with several malware scanning programs on the Windows computer.
Please scan with all programs because each program detects different malware.
All these programs have free versions.
Make sure that you update each program to get the latest version of their databases before doing a scan.
*Malwarebytes' Anti-Malware:<br>http://www.malwarebytes.org/mbam.php
*AdwCleaner:<br>http://www.bleepingcomputer.com/download/adwcleaner/<br>http://www.softpedia.com/get/Antivirus/Removal-Tools/AdwCleaner.shtml
*SuperAntispyware:<br>http://www.superantispyware.com/
*Microsoft Safety Scanner:<br>http://www.microsoft.com/security/scanner/en-us/default.aspx
*Windows Defender:<br>http://windows.microsoft.com/en-us/windows/using-defender
*Spybot Search & Destroy:<br>http://www.safer-networking.org/en/index.html
*Kasperky Free Security Scan:<br>http://www.kaspersky.com/security-scan
You can also do a check for a rootkit infection with TDSSKiller.
*Anti-rootkit utility TDSSKiller:<br>http://support.kaspersky.com/5350?el=88446
See also:
*"Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked