"Even if your initial response is a resounding "meh" --
there are other web office suites, such as Google Docs, and even
the Ulteo Linux/OpenOffice suite -- there are just so many other
implications in Microsoft's making this available for Firefox,
never mind Safari and the Linux operating system.
"Is it an unspoken acknowledgement that open source software and
systems are popular, and prevalent enough that neglecting to
support them would be -- foolish? Even more alienating? Financially
damaging? Giving Google the upperhand? All of the above?"