1. Open prefs framework demo: http://build.fluidproject.org/infusion/demos/prefsFramework/
2. Set the preference "colour and contrast" to apply a theme that has black or grey background;
3. Use keyboard to tab onto "reset" or "hide" links. The focus styling is invisible for the black background themes and hard to see for the grey background (with a black border focus styling).
Other separated panel demos don't have this problem and this issue only occurs in firefox.