Bug 891081 Change Private Browsing shortcut key as it conflicts with spellcheck r=Ratty

a=Callek for checkin to a CLOSED TREE

suite/locales/en-US/chrome/common/utilityOverlay.dtd

@@ -23,7 +23,7 @@
 <!ENTITY newNavigatorCmd.key "N">
 <!ENTITY newNavigatorCmd.accesskey "B">
 <!ENTITY newPrivateWindowCmd.label "Private Window">
-<!ENTITY newPrivateWindowCmd.key "P">
+<!ENTITY newPrivateWindowCmd.key "B">
 <!ENTITY newPrivateWindowCmd.accesskey "W">
 <!ENTITY printSetupCmd.label "Page Setup…">
 <!ENTITY printSetupCmd.accesskey "u">