Firefox pop up led to pc uploading system files to ??

Using Firefox ver 9 yesterday got a pop up box saying I needed to upgrade Firefox. I clicked the button.

The screen didn’t change but after a few seconds, I noticed an area upper right with scrolling file names. %Windows% caught my eye. I switched off my wireless antenna quickly.

The address line showed www.softochck.org. I quickly closed the window.

Is There any way to see what was uploaded, and why or by who?

Windows xp sp3, wireless connection to Internet in our office.
I run paid version of avg, it did nothing, no prompt or question.

Any advice appreciated.