Web browser pops up scripts opened from Bluefish

Hello,

I installed Bluefish editor couple of days ago. In toolbar there is icon that says. "preview in browser". But when I want to preview some php script, it pops up in web browser (Firefox) and asks me if I want to save or open script. What can I do to fix that and scripts start opened from "bluefish" to execute in web browser instead of this popping-up?

Thank you for answering my question.