Backout ac2581b910b6 (bug 823547) and f50b8afa272f (bug 820834) for bc failures in browser_aboutHome.js
Bug 845887 - upload new talos.zip to capture recent talos changes. r=aki
Bug 844970 - Use a grace period for all process priority downgrades. r=cjones
Bug 834672 - AppProtocolHandler.js should never throw r=jduell
Bug 844530 - Paper over error in BrowserElementPromptService.jsm on B2G. r=khuey

The error we're fixing is

  E/GeckoConsole(  397): [JavaScript Error: "NS_ERROR_FACTORY_NOT_REGISTERED: Component returned failure code: 0x80040154 (NS_ERROR_FACTORY_NOT_REGISTERED)
  [nsIComponentManager.getClassObject]" {file: "resource://gre/modules/BrowserElementPromptService.jsm" line: 572}]

For some reason, we're running code before the vanilla prompt service is
instantiated.  We don't know why this is happening, but this patch works
around the problem on B2G, which is the only place where we ship this
code.