Silverlight installation per machine/browser?

A question I had on top of my head:
When you install Silverlight, is it installed automatically on every browser available on your machine or is it per browser like Flash installation ?

The answer is:
"When you install Silverlight, it installs itself for both Firefox and IE on Windows, and both Safari and Firefox on Mac, regardless of what browsers you currently having running or installed."
Thanks to Daniel Harvey from the silverlight.net forums.