how can I save a file from firefox to /opt/subdir/ on a mac

In firefox when I right click (mac: Control+left click) to bring up the context menu and click “Save link as” firefox on mac pops up a dialog box. (dialog box prompting save file in firefox on mac). If I set the destination to the system drive, and expand the location picker on the left side it lists:

  • applications
  • library
  • system
  • users

But there’s no /opt/ listed there. I want to store the file in /opt/mysubdir/.

Is it possible?

Do I need to start firefox with sudo?