the fiddler2.com issuer in certificates is usually a sign of unwanted malicious software present on your pc that is intercepting secure network traffic. please go into the system control panel and uninstall programs like BrowserSafeguard, BrowserSafe, SafeGuard or other software that sounds suspicious and didn't get installed by you intentionally. _{reference: https://support.mozilla.org/en-US/questions/982532#answer-520145} afterwards, run a full scan of your system with different security tools like the [http://www.malwarebytes.org/products/malwarebytes_free free version of malwarebytes] & [http://www.bleepingcomputer.com/download/adwcleaner/ adwcleaner]. [[Troubleshoot Firefox issues caused by malware]]