Firefox Update with BITS download

[Kirk Steuber]

Exciting changes are coming to Firefox Update on Windows!

We have added the ability to download updates via the Windows BITS
component. This change will allow Firefox to continue downloading an update
after Firefox has been closed. Note that this does not allow downloads to
be started without Firefox (but that feature is in the works!)

This feature is already on Nightly, but is turned off by default. It can be
enabled by setting the "app.update.BITS.enabled" pref to true.

Soon, we plan to test this feature by turning it on for a randomly-selected
half of Nightly users. This will be done by setting the default value of
the pref, so the decision can still be overridden by changing the pref
value manually.

If you have a problem with this feature, you can file an application update
bug blocking Bug 1540193:

https://bugzilla.mozilla.org/enter_bug.cgi?product=Toolkit&component=Application+Update&blocked=1540193

-bytesized