Post review followup to bug 335154 mentioned by Neil on irc, remove extra full stop that shouldn't have been there.

suite/debugQA/locales/en-US/pref-debug.dtd

@@ -11,7 +11,7 @@
 <!ENTITY debugStrictJavascript.label     "Show strict JavaScript warnings">
 <!ENTITY debugConsoleJavascript.label    "Show chrome JavaScript errors and warnings">
 <!ENTITY debugUseXBLForms.label          "Use XBL-based form controls (takes effect after restart). These are still under construction.">
-<!ENTITY dynamicSkinSwitching.label      "Enable Dynamic Skin Switching.">
+<!ENTITY dynamicSkinSwitching.label      "Enable Dynamic Skin Switching">
 
 <!-- Debug: Turn on gfx-rendered widgets -->
 <!ENTITY widgetRendering.label "Rendering">