Setting Firefox's directory for files to be opened (instead of "saved")

How do I set the folder to which Firefox saves files which I wish to open immediately? I thought it was the folder I set for downloads in Safari, but I changed that and Firefox still used ~/Downloads for files that Firefox opens (instead of "saving"). I am pretty sure it was Safari's directory setting that it used for this but it's not working. Is it because I'm Leopard now?

 

No; that directory is where Firefox saves files, as in where it puts the files that you select "save to disk" for in the dialog that appears after you click the download link. I am talking about the directory in which Firefox puts the files for which you select "open with..." Those are not the same directories and in the past, if I remember correctly, the only way to change this directory was in Safari.