Backed out changeset f8cccf3de0a3 (bug 842495) for crashtest failures on a CLOSED TREE.
Bug 824891 - Change |result| from XML_Error to XML_Status to quell some -Wenum-conversion warnings.  r=jst,peterv.

--HG--
extra : rebase_source : e367d5eb46d7e101298b1517439ca6f1f723e0f3
Backed out changeset c6c6535fb6c2 (bug 844530) for Marionette failures on a CLOSED TREE.
Bug 755126 add social services management to about:addons, r=felipe
Bug 841477 - Enable FAIL_ON_WARNINGS on MSVC in dom/plugins. r=benjamin
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.