The headline is completely wrong and somehow links to something that isn't the actual discussion, which is here: https://groups.google.com/forum/#!topic/mozilla.dev.apps.fir...

Here's further explanation from the opening poster of that thread:

For the purposes of this thread, it is already a done decision that we aren't going to ship 64-bit Windows Firefox builds in the first half of 2013, and probably not at all in 2013. In the meantime, we aren't going to fix crashes or plugin bugs that only affect 64-bit builds. Those decisions have already been made. The only question to decide here is whether the existing 64-bit Windows nightlies provide any value to the project.

They're not discontinuing 64-bit Firefox on Windows; they haven't even released it yet. They do intend to release it, but probably not until 2014.