I was thinking of "fine tuning" from the about:config page
to prevent sites from seizing control of your buttons and so forth.
It seems that the dialog boxes had a "global grab" so nothing else worked.
I couldn't change tabs, or even close the browser window. Of course I could
go to another desktop (gnome) open a terminal and kill firefox. What would happen if the site was truly malicious? I'm sure there are some subtle things
you can do short of blocking scripts entirely.