Firefox error code sec_error_unknown_issuer
What is ‘Firefox error code sec_error_unknown_issuer’?
“Firefox error code sec_error_unknown_issuer” is an error that may occur when the certificate provided is issued by a certificate authority that is not known by Firefox and cannot be trusted by default.
How can you fix ‘Firefox error code sec_error_unknown_issuer’?
Some of the common fixes include:
- Disabling extensions and third-party programs
- Scanning for malicious software
- Disabling the network proxy
Please see our in-depth walk-through solutions below.
Solution 1. Disable Extension and Third-party program
“Firefox error code sec_error_unknown_issuer” may appear when your communication with the website is intercepted or injected by unknown data caused by a third-party software. This could be caused by a security software, browser extension/ add-on or malicious software. To fix the problem, you may want to try disabling all running third-party programs by booting your operating system in clean boot and removing or disabling all Mozilla Firefox extensions/ add-ons. See steps below.
Step 1. Disable/ Remove Extension/ Add-on
- Open Mozilla Firefox.
- Click Shift+CTRL + A keys, to open about:addons page.
- Click the Extensions.
- Disable or Remove all Extension/ Add-on.
Step 2. Clean boot (watch the video below)
If the issue persists, try to scan your computer with an updated anti-virus.
Solution 2. Scan for malicious software
It is possible that the cause of “Firefox error code sec_error_unknown_issuer” is a malicious software, injecting an unknown data to steal information from you. To confirm, run an updated anti-virus and do a full scan of your system. If you do not have any anti-virus, check this link here to aid you to decide what legit antivirus software best work for you. If the antivirus is ready, check for an update before doing a full scan of your system.
It may take a while. After the scan, restart your computer then try to browse again using Mozilla Firefox.
Solution 3. Disable Network Proxy
“Firefox error code sec_error_unknown_issuer” could also be caused by your proxy setting, Try to set it to default settings to fix the problem. See instructions below.
- Open Mozilla Firefox.
- In the address bar type about:preferences#general and press Enter key.
- Scroll down look for Network Proxy and press Settings.
- InConfigure Proxies to Access the Internet, select Use system proxy settings or No proxy.
Watch the instruction here on YouTube or refer to the image below.