neowin.net/news/firefox-64-bit-is-now-available-to-download
The update to the 32 bit browser as usual appears on the About screen.
Note: When you run a 32 bit app [the vast majority of software available] Windows 64 bit runs many duplicate processes using 32 bit versions of Windows files. That is inherently less secure, e.g. it's been shown that it's possible to bypass the mitigation toolkit. Microsoft is aware if it, but any fix would require some major restructuring of Windows.
threatpost.com/latest-emet-bypass-targets-wow64-windows-subsystem/115224/