Did you get those errors when using the advanced search page, or just the normal search pop-up box? And approximately how often does this happen?
I tried doing a few dozen searches just now (from the search pop-up box, not the advanced search page), and I couldn't reproduce the error (firefox 3.5). There's got to be some other factor.
Also (peetza) it looks like both your firefox and safari versions aren't the latest. I'm sure that has nothing to do with it, just mentioning it because new browser versions often fix security problems...
“The egg hatched...” “...the egg hatched... and a hundred baby spiders came out...” (blade runner)
“Who are you?” “A friend. I'm here to prevent you from making a mistake.” “You have no idea what I'm doing here, friend.” “In specific terms, no, but I swore an oath to protect the world...” (continuum)
“It's a goal you won't understand until later. Your job is to make sure he doesn't achieve the goal.” (bsg)