Middle-click and drag doesn't trigger auto scrolling

The function you describe is called 'autoscroll' and it's an option you can enable in Firefox. Check the preferences menu, it's in there.

It's not a system bug, just one of the ways things are different on Ubuntu (and Linux in general) compared to Windows. Middle-click is used to paste from the xclipboard -- this is distinct from the Ctrl+C/Ctrl+V clipboard you are probably used to. Any text you highlight with your mouse will be available to paste by middle-clicking.

This may not sound useful at first, but it really is -- middle-click paste is one of those small things that I really miss when I have to use Windows.

This is handled by Ubuntu rather than any individual program, so using a different version of Firefox won't help you. I'm sure it is possible to enable the behaviour you're describing, but it would probably be quiet a lot of effort.