Which security software (firewall, anti-virus) do you have?

Some security software has virtualization features that can cause problems by protecting and restoring files in the Firefox profile folder.

After years of BlackIce Defender and Norton, I only use my ISP provided ones (Bell here in Canada), and to my knowledge, there has been no change in anything on that end, but I will certainly look into it, thanks.

It just happened again, and this was the process: Firefox wasn't responding (may have been a memory issue, as I also had Photoshop and a few other things open), so I closed it by right clicking on icon. I waited a few minutes, clicked on the icon to re-open, and it told me that I needed to reboot to continue an installation of Firefox (even though the latest version loaded fine today). After I rebooted...there was the 3.6.27 version. Again. No idea where it would be getting this version, I don't see a download, and I certainly don't have a copy.

The only thing I can think of that has been a bit weird lately: I downloaded a version of Calibre for my Kindle, and when I went to close my wife's IE Explorer, I noticed that Babylon search toolbar was there. After nuking that garbage (via registry), it was gone. Not sure if that is relevant, though.