Whoa, when did I install Silverlight?

I like to consider myself a safe web surfer, as I am very knowledgeable about computers and use safe surfing habits, but I was just shocked by something that occurred a short while ago.

During a normal run around the internet, nothing too out of the ordinary, I popped the start menu to grab the calculator for some quick mathematical assistance, when I noticed, at the bottom of my list was Silverlight. Now, I knew that wasn't there earlier, and I have been avoiding Silverlight since it's inception as it is completely unnecessary software. I have Automatic Updates set up to simply notify me when there are updates available, and I pick and choose which to install. I had not updated anything recently. I had not installed new applications recently. I checked the shortcut properties to see when it was created, and was shocked to see it was made a mere 4 minutes ago. I was just surfing the internet then... in Firefox no less... how did this happen? I checked the event viewer and saw two related entries, 4 minutes before. One said

Product: Microsoft Silverlight - Update 'Microsoft Silverlight 3.0.50611.0' installed successfully.

The other (clocked at the same second) said

Product: Microsoft Silverlight -- Configuration completed successfully.

What?

Regardless, I uninstalled it as quickly as it had mysteriously appeared, but am still a little unsure of my security. Comodo didn't even peep at me about it... and it even peeps when Defender gets updated definitions. Has anyone else experienced drive-by Silverlighting?
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Big Cray: Accept No Substitute