The F-secure
online scanner is safe. There will be a security alert to install an activex control, an add-on for Firefox, which then needs to be restarted.
I'm surprised S&D thought it was unsafe. Was this the tea-timer alerting to a reg change? If so, allow it. Better yet, disable the Tea-timer.
Here is a list of FAQ's fro the scanner.
It's commonly recommended/used on some of the security sites I frequent, as part of a cleanup routine.
Now the question comes: Why do you want to run it?
Problems, Don't trust your resident AV, or just want a second opinion?