Are you installing from Mozilla's site? How to download and install Firefox on Mac

thank you for responding. My MacBook air came with firefox already installed. When I click on it, I get the box saying I have to install Rosetta. I don't understand this. thanks again

Sorry, as a Windows person, I have no idea what Rosetta is for. You could try removing that Firefox and reinstalling a normal version of Firefox in case that's a customized one.

thanks. I'll give that a try