If you have recently updated to Firefox version 58, you may have noticed an annoying error code when visiting websites. ‘SEC_ERROR_UNKNOWN_ISSUER’ (Your Connection is Not Secure) isn’t all that common, however, after updating Firefox, you may start to see it more frequently, even on popular websites like Google.com. Thankfully there are a few simple ways you can fix the issue.


How to Disable Telemetry Data Collection on Firefox Quantum.

Although Firefox is the underdog in the browser market, it is one of the best browsers on the market. It’s fast, has a very clean interface, and uses significantly fewer resources than the top dog Chrome. As good as it is though, Firefox does have an annoying bug/error which affects a small percentage of users.

Error ‘SEC_ERROR_UNKNOWN_ISSUER’ has been around for quite some time, however, was very rare to see on Firefox 57, in most instances the issue was caused by the websites settings and not Firefoxes. Thankfully, regardless of the reason you are seeing this error message, there are a few different ways you can fix it.

How to Fix 'SEC_ERROR_UNKNOWN_ISSUER' & ‘Your Connection is Not Secure’ Error Messages on Firefox 58.

To remove this error from Firefox there are two different options available. The first is to add an exception for the website to your Antiviruses exception list. The second is to disable SSL/HTTPS scanning, again in your antivirus settings. Option one is by far the least risky and doesn’t open up a potential security flaw in your system. Option two, however, will save you having to add every website to the exception list. Before using either of these steps, make sure you have uninstalled Firefox and reinstalled it from scratch. If you are using a Firefox account it won’t take much time at all to set up your browser again.

Note: You can also try browsing the website using a New Private Window by right-clicking on the Firefox icon and selecting New Private Window.

How to Add Websites to Your Antivirus Exception List to Fix Firefox ‘SEC_ERROR_UNKNOWN_ISSUER’ & ‘Your Connection is Not Secure’ Errors.

This process will differ a little depending on the antivirus program you are using, however, the option should be under a very similar heading. Below you will find an example of how to add a website to Avast’s exceptions list. To begin open Avast, stay on the Status tab, then click Settings at the bottom of the page.


On the next page stay on the General tab and expand the Exclusions section using the drop-down arrow. Now simply change to the URLs tab and add the website you can’t get access to, to the list.

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Note: Depending on the website, Firefox may allow you to add an exception directly from the error message. Simply click Advanced > Add Exception and manually add the website URL.


How to Disable SSL/HTTPS Scanning to ‘Fix SEC_ERROR_UNKNOWN_ISSUER’ & ‘Your Connection is Not Secure’ Errors on Firefox 58.

As we mentioned above, this isn’t the most recommended or safest solution, but it will get rid of the error on your browser. (Again these steps will vary somewhat depending on the antivirus software you are using). Below you will find an example of how to add a website to Avast’s exceptions list.

Open Avast, stay on the Status tab and click Settings at the bottom of the page.

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Next, change to the Components tab and click Customize next to Web Shield. 

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On this screen stay on Main Settings and Untick the box next to Enable HTTPS Scanning. Once this is done, click Ok to save the changes. As mentioned above, if you can avoid using this method it is suggested, however, if you don’t want to change browsers and don’t mind the security risk, feel free to make the change.

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