It seems Benjamin Smedberg has had a change of heart (or was it all the negative feedback) in his earlier decision to discontinue the Firefox 64-Bit Windows builds.

After I announced my decision to disable 64-bit Windows nightlies, there was significant negative feedback. After reviewing that feedback, and consulting with Release Engineering, I believe that we can keep a set of users happy by making a modification to the original plan.

At this point, the Mozilla project does not have the resources to actively support this use case. Making these builds, however, is not a
significant burden on our Release Engineering group.

Well, this certainly explains why for the past month I have still continued to get Nightly updates for my Windows 64-Bit Firefox.

See the Google Groups posting for more details.