There's an important difference between Linux and Windows, however: on Linux, "long" is always as wide as a pointer, while on 64-bit Windows, a pointer won't fi

There's an important difference between Linux and Windows, however: on Linux, "long" is always as wide as a pointer, while on 64-bit Windows, a pointer won't fit in a "long" or "LONG" or "DWORD". But the real reason 64-bit Firefox is the default on 64-bit Linux, is that 64-bit Linux usually doesn't have the 32-bit compatibility libraries installed by default. On Windows, on the other hand, 32-bit compatibility libraries are always available.