Linux and Mac users have enjoyed having a 64-bit versions of Firefox available to them for nearly the past two years. However, for us Windows users, Mozilla has been
teasing us and/or dragging their feet with 64-Bit Firefox. As a point of clarification I should say that there has been since Firefox 4 (may be even further back) 64-bit
Windows builds on the Nightly Developmental channel. These are not official releases and have never made into the Aurora or Beta stage, much less release. There has been some progress moving towards a Win 64-bit Firefox in that most (if not all) the popular Windows based Plugins (Flash, Java, Silverlight, etc.) are now available in 64-bit versions. Also, Mozilla has moved over recently to Microsoft Visual C++ 2010 compiler, still there is a lot of work that needs to be done before there will be an official Windows 64-Bit Firefox release.