32-bit Firefox on 64-bit Ubuntu

After months of awkward hacks to work around the lack of 64-bit Flash, Java and RealPlayer plugins for Firefox on Linux, finally these simple instructions work straight away.

Basically Ubuntu provides a bunch of 32-bit libraries that go in /lib32 and /usr/lib32. When you prefix a command with linux32, it pretends to an application that it's running in a 32-bit environment.