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.
Most importantly, it seems that there are users who regularly run into 
the 4GB memory limits of 32-bit builds. These users often have hundreds 
or even thousands of tabs. These users are using the 64-bit nightlies 
not primarily to be part of our testing community, but because those 
builds are the best product available.
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. Therefore I have 
modified my original plan in the following way:
* Migrate all existing users of win64 nightly channel builds to the 
win32 nightly channel builds via automatic update.
* Continue to build win64 Nightly builds and updates on the nightly 
channel. Users who need the 64-bit builds will have to download it after 
the migration point (date TBD).
** Change the default first-run and update page for win64 builds to 
explain to users that they are not supported.
** Disable the crash reporter for win64 builds
** Enable click-to-play plugins by default in the win64 builds.
* Discontinue the win64 tests and on-checkin builds to reduce release 
engineering load. By default, do not generate win64 builds on try.
* win64 builds will be considered a �tier 3� build configuration. [1]
We will continue to test the win32 builds and make sure that they work 
well on both 32-bit and 64-bit versions of Windows. Specifically, all of 
our testing on Windows 8 is planned to be done on the 64-bit version of 
Windows 8.
I do hope that the projects and developers who are interested in win64 
will work together to maintain this build configuration. I am interested 
in hearing from volunteers who want to become the 64-bit build 
maintainer. I will also set up a discussion list specifically for win64 
issues, if that would be valuable.
--BDS
Please post followups to to mozilla.dev.apps.firefox
[1] 
https://developer.mozilla.org/en-US/docs/Supported_build_configurations