Do they fully fill the tanks for the static fire, or just put in the minimum to chill down everything and run the test?
Full tanks, because that is the lift off conditions. Even the second stage will be tanked and it doesn't fire.
so probably the more appropriate question would be what are the differences, if any, between the static fire conditions and launch conditions, apart from the obvious (e.g. hold down mechanisms not set for release and engines set to cut-off after 2 seconds)?