Bug 1077652 - Introduce new preloading mechanism
Bug 1077652 - Update browser_newtab_background_captures.js to work with the new preloader
Bug 1077652 - Revert change from bug 794041 that makes test_docload.html expect accessibles in the hidden window
Bug 1077652 - Let a11y tests know about the extra preloaded document
Bug 1077652 - Remove old BrowserNewTabPreloader.jsm and references r=jaws