Bug 1109802 - Release IAudioStreamVolume after use in libcubeb's WASAPI backend. r=padenot, a=lsblakk
Bug 1106584 - Part 1: Guard against null intent. r=vng, a=lsblakk
Bug 1106584 - Part 2: For safety, make explicit prefs with context getter. r=vng, a=lsblakk

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 1106252 - Make nsImageFrame's icon loading code more robust. r=tn, a=sledru