Bug 1077652 - Introduce new preloading mechanism r=dao
Bug 1077652 - Update browser_newtab_background_captures.js to work with the new preloader r=adw
Bug 1077652 - Revert change from bug 794041 that makes test_docload.html expect accessibles in the hidden window r=tbsaunde
Bug 1077652 - Let a11y tests know about the extra preloaded document r=tbsaunde
Bug 1077652 - Remove old BrowserNewTabPreloader.jsm and references r=jaws
Bug 1104927 - UITour: Add Loop conversation view target for email/copy link buttons. r=Unfocused,mixedpuppy
Bug 1016825 - Show legacy-Sync-to-Firefox-Accounts migration notifications in the main browser window. r=markh
Bug 1104927 - UITour: Update browser_UITour_loop.js with for Loop:ChatWindowShown. r=me
Bug 1106584, Part 1: guard against null intent. r=vng
Bug 1106584 - Part 2: for safety, make explicit prefs with context getter. r=vng

Any class that has access to a context should call Prefs.getInstance(Context) which is guaranteed to return a Prefs.
With no context, classes can call Prefs.getInstanceWithoutContext() but they must null-check the return, and handle accordingly.
Fortunately, the latter case happens in very few places, all of which require no special handling of this case.

This change:
- maintains context-less access to the Prefs
- classes internal to the service can safely call getInstanceWithoutContext(), as the service (or the MainApp in the stumbler case)
will have instantiated a Prefs so that getInstanceWithoutContext() will return a prefs
- protects against null Prefs if we have failed to consider a particular entry point to the code will require that Prefs was instatiated with a context.
Bug 1109233 - Replaced Assert.isTrue(false, ...) with Assert.fail(...) for easier readability; r=mcomella
Bug 1109112 - Avoid highlighter exceptions after reloading the page; r=miker
merge fx-team to mozilla-central a=merge