Mozilla Firefox verifies the certificates of websites that support secure browsing. If Firefox cannot validate the security certificate of multiple sites, you might run into an error page that denotes the issuer of the certificate is unknown to Firefox. Consequently, your connection to the website is not secure. If the error pops up on multiple legitimate websites that allow financial transactions, refer to the first two steps below. If it is specific to a particular website, read on for troubleshooting steps for SSL errors.
If you come across such errors, it is also likely an antivirus suite’s scanning secured connections feature has replaced the legit site’s certificate with its own. If that is the case, you should disable the antivirus software’s feature from its settings.
Malicious software can not only cause Firefox freezes every few seconds but also the SEC_ERROR_UNKNOWN_ISSUER error. In fact, some malware types intercept secured web traffic on a browser and cause the said error message to appear on multiple sites. To clear the browsing inconvenience, scan for and remove malware on the computer.
This step is applicable if the error pops up while browsing on Firefox over a public network. If the description of the error suggests that an intermediate certificate is not found, enter its hostname into an online service that tests SSL web server’s legitimacy. If the third-party SSL testing page returns Chain issues: Incomplete, a legit intermediate certificate is certainly missing. If that is the case, inform the website about the missing certificate. To get the description, click on Advanced button on the web page that states the connection is not secure.
If the description suggests that the certificate missing issue on a website accessed over a private network is due to the fact that it is self-signed, bypass the error with the below steps. This can be done provided the intranet website allows adding an exception for visiting the site, despite the certificate not trusted by default by Firefox.
If you still come across Firefox freezes every few seconds issues or any other SSL errors, contact a browser support team to fix the problem.