add an article on fixing the Mozilla error

docs/adguard-for-windows/solving-problems/mozilla-error.md

@@ -0,0 +1,31 @@
+---
+title: How to fix the `MOZILLA_PKIX_ERROR_KEY_PINNING_FAILURE` error
+sidebar_position: 11
+---
+
+:::info
+
+This article covers AdGuard for Windows, a multifunctional ad blocker that protects your device at the system level. To see how it works, [download the AdGuard app](https://agrd.io/download-kb-adblock)
+
+:::
+
+Some users of AdGuard for Windows with enabled [HTTPS filtering](/general/https-filtering/what-is-https-filtering) are unable to access certain websites like google.com and youtube.com. Instead of opening a website, browsers with Strict Certificate Pinning would display a `MOZILLA_PKIX_ERROR_KEY_PINNING_FAILURE` error.
+
+Here is a list of impacted browsers:
+
+- Arkenfox
+- Brace
+- Cachy Browser
+- Dove
+- FireDragon
+- LibreWolf
+- Mull
+- Mullvad Browser
+- Phoenix
+- Tor Browser
+
+If your default browser is one of these, do the following to solve the problem:
+
+1. Type `about:config` in the address bar of your browser
+1. In the menu that appears, enter `security.cert_pinning.enforcement_level` in the search field.
+1. Change the `security.cert_pinning.enforcement_level` parameter from 2 to 1.

docs/adguard-for-windows/solving-problems/solving-problems.md

@@ -21,3 +21,4 @@ Here are some problems you may encounter and workarounds, guides, and instructio
 - [How to create a dump file](/adguard-for-windows/solving-problems/dump-file/)
 - [Possible DNS leaks](/adguard-for-windows/solving-problems/dns-leaks/)
 - [Known issues of AdGuard for Windows](/adguard-for-windows/solving-problems/known-issues/)
+- [How to fix the `MOZILLA_PKIX_ERROR_KEY_PINNING_FAILURE` error](/adguard-for-windows/solving-problems/mozilla-error/)