Ok, got it. But the website doesn't mention it at all. You have to browse the server directly to get it. Looks like they don't really want their users to install it.
My Firefox just updated to version 42. Did it sense that I'm running a 64-bit Win-10 O.S. and update me to the new 64-bit version? How can I tell if this new/updated version is 64-bit or 32-bit?
Run it and take a look at the task in task manager. 32 bit programs got a "(32 bit)" remark. If there is no such remark it's a 64 bit program.
I use Chrome as a default browser on the 4 PC's here but aside from the sandbox thing F/F is decent .
On the daily driver here I have F/F on my other primary partition in Windows 10 RTM along with Chrome ,IE 11 and Edge >
( the red headed wonky Windows 10 /IE11 stepchild .) ☻
I will likely update to the 64 bit F/ F though since I came across this thread sometimes F/F comes in handy .