I've downloaded the new version, and when I go to drag the Firefox icon into the Applications folder, I'm prompted to replace the old version. When I do, it says, "The operation can’t be completed because you don’t have permission to modify 'Firefox'." I've looked everywhere, and every help forum says to just drag Firefox into the Trash. I've tried that, and it says that Firefox can't be trashed. I don't know if this means anything or not, but there is a small lock in the bottom left of the Firefox icon in my dock.