Fix #3160, remove app startup delay
Fix #3160, remove app startup delay

The 'sessionstore-windows-restored' delay is now applied to all
extensions by the addon management code in Firefox. See bug 1457224
for details.

mozilla-services/pageshot,mozilla-services/screenshots,mozilla-services/screenshots,mozilla-services/pageshot,mozilla-services/pageshot,mozilla-services/pageshot,mozilla-services/screenshots,mozilla-services/screenshots