It seems that it isn’t only Firefox that is stuck in 32-bit on Windows. The only Windows 8 browser that runs by default as 64-bit code is the Metro version of IE. Wonder if it is coincidence that the Metro IE doesn’t support plugins; maybe plugin compatibility is at the root of this.

Oh, and why do Microsoft keep up the 32-bit version of Windows? Because they are determined to be all things to all people, and as an organisation seem unable or unwilling to cut off support for older hardware.