Certificates trust issues in Firefox browser

For AdGuard to successfully filter HTTPS traffic in Firefox, the browser needs to trust AdGuard's certificate. It can be achieved differently for different versions of the Firefox.

Method 1

This method works in Firefox for Android version 90.0 and later.

To make Firefox trust the AdGuard certificate, do the following:

1. Run the browser.
2. Go to Settings > About Firefox.

3. Tap the Firefox logo five times.
4. Navigate to Settings > Secret Settings.

5. Toggle Use third party CA certificates.

Method 2

This method will only work on rooted devices.

1. Install and configure adb;

   On the Windows platform, Samsung owners may need to install this utility.

2. Activate the developer mode and enable USB debugging:
   • Open the Settings application on your phone;
   • Go to System section (last item in the settings menu). In this section find sub-item About phone;
   • Click on the Build number line 7 times. After that, you will receive a notification that You are now a developer (If necessary, enter an unlock code for the device);
   • Open System Settings > Developer Options > Scroll down and enable USB debugging > Confirm debugging is enabled in the window Allow USB debugging after reading the warning carefully.
3. Install the Firefox browser (release version);
4. Open the AdGuard settings > Network > HTTPS Filtering > Install the certificate in Firefox > INSTALL FOR OLD VERSIONS;
5. Open the folder data/data/org.mozilla.firefox/files/mozilla using adb shell su and cd data/data/..., then browse to the folder named xxxxxxx.default and memorize its name;
6. In the specified folder we are interested in two files:
   • cert9.db
   • key4.db
7. We need to move these files to a folder of the browser where the security certificate issue occurred:
   • data/data/org.mozilla.<browser_name>/files/mozilla/yyyyyy.default.
8. The full command will look like this:
   • adb shell su
   • cp -R data/data/org.mozilla.firefox/files/mozilla/xxxxxxxxxx.default/cert9.db data/data/org.mozilla.<browser_name>/files/mozilla/yyyyyyyyyy.default.
   • cp -R data/data/org.mozilla.firefox/files/mozilla/xxxxxxxxxx.default/key4.db data/data/org.mozilla.<browser_name>/files/mozilla/yyyyyyyyyy.default.

In case you received the system notification permission denied, you should first move the specified files to the permission-free directory. And after that you should move them to the necessary folder in your Firefox browser.

The full command should look something like this:

• adb shell su.
• cp -R data/data/org.mozilla.firefox/files/mozilla/xxxxxxxx.default/cert9.db sdcard/Download
• cp -R data/data/org.mozilla.firefox/files/mozilla/xxxxxxxxx.default/key4.db sdcard/Download
• cp -R sdcard/Download/cert9.db data/data/org.mozilla.<browser_name>/files/mozilla/yyyyyyyyyy.default.
• cp -R sdcard/Download/key4.db data/data/org.mozilla.<browser_name>/files/mozilla/yyyyyyyyyy.default.

If adb shell su does not work, you should try adb shell initially, and then su.