Using Norton Safe Web Lite.
When a Norton Site Safety message pops-up because of entering a website rated red by Norton it disappears when the mouse is clicked. I have the Norton Toolbar hidden in Firefox and only rely on these pop-ups to warn me. The pop-up appears when the website has fully downloaded and if you click anywhere on the browser as the same time as the pop-up appears you are likely to not see the pop-up.
The Site Safety warning should display until the user clicks the x.
If you go to a different tab before the website fully loads, no pop-up will appear when you go back to that tab. I hope this will be changed too.