Open Firefox and navigate to about:config: Type about:config in the Firefox address bar and press Enter. You might get a warning message; proceed by clicking "Accept the Risk and Continue".
Search for the preference: In the search bar, type security.enterprise_roots.enabled.
Toggle the preference: If the value is false, click the "Toggle" button (or double-click the line) to change it to true. This will enable Firefox to use the system's certificate store.
Restart Firefox: After making the change, restart Firefox for the setting to take effect.