Mark and I think that unchecking "Custom Values" in the Security Slider should immediately cause the descriptive text to be displayed for the selected level. Steps to reproduce: 1. Open about:config and toggle a security-related pref.(e.g., svg.in-content.enabled). 2. Open the Privacy and Security Settings window. Uncheck "Custom Values". The text is displayed immediately if a new level is chosen via the slider or if "Restore Defaults" is clicked.