It looks like FireFTP switches from "Automatic Mode" to "ASCII Mode" after installing the latest Firefox update (v3.6.15).  Check for this if you're uploading images or other binary files and they're not rendering on the web server.  The error you may see in the browsers is, "The image cannot be displayed, because it contains errors."  The fix is just to switch back to auto in the settings (FireFTP > Tools > Downloads/Uploads).