Add brandShortName to content pack switch message.

b=109477; sr=alecf

extensions/content-packs/resources/locale/en-US/pref-contentpacks.dtd

@@ -1,6 +1,6 @@
 
 <!ENTITY lHeader                        "Content Packs">
-<!ENTITY contentIntro.label             "Selecting a new content pack changes items in the Sidebar and the Search menu, and changes the home page, certain bookmarks, and other items. You will not lose bookmarks and other items that you have customized when you switch content packs. You must restart for a new content pack to take effect.">
+<!ENTITY contentIntro.label             "Selecting a new content pack changes items in the Sidebar and the Search menu, and changes the home page, certain bookmarks, and other items. You will not lose bookmarks and other items that you have customized when you switch content packs. You must restart &brandShortName; for a new content pack to take effect.">
 <!ENTITY installedContentPacks.label    "Installed content packs:">
 <!ENTITY downloadContentPacks.accesskey "d">
-<!ENTITY downloadContentPacks.label     "Download More...">
+<!ENTITY downloadContentPacks.label     "Download More...">