The proposal of striking off the 64-bit nightly builds was put forward by Benjamin Smedberg, a Firefox developer, last week. Some of the reason that Smedberg cited for constant frustration include missing plugins for 64-bit version; lack of windowproc hooking which facilitates smooth functioning of whatever plugins are available; and inability to work on the crash reports submitted for the 64-bit versions because they were not on high priority.
The proposal, it seems, has been accepted as is evident from this bug report. The decision about not going forward with the 64-bit variant of Firefox has its root in an investigation carried out by Firefox Product Manager Asa Dotzler which concluded in March this year.
In an email to the Mozilla Development mailing list, he concluded that it was not the right time to promote and elevate the 64-bit Windows version of the Firefox browser to an official release but, rather to go ahead with nightly builds only and that it should be kept as of now as an experimental version.
Smedberg’s suggestion met with a lot of opposition but, Firefox pointed out that they do not have enough resources that can be spared to deal with 64-bit specific bug reports. Further it was also revealed that they wanted to put their efforts in making the 32-bit version better. "Given the people constraints imposed by those projects as well as Firefox OS, we do not have the ability to fix the remaining bugs in win64 builds or turn them into a production release. We need to focus our testing community on the things which are most important." notes Smedberg in an email.