STR: 0. Ensure that the downloads pref on the general pane of about:preferences is set to "always ask"; 1. Open Firefox 2. Open browser debugger 3. Open http://www.apple.com/it/itunes/download/ 4. Click the download button 5. As the "What do you want to do with this file" dialog comes up, go to the browser debugger, and load nsHelperAppDlg.js ER: See the source AR: It shows: dialog.postShowCallback() and nothing else. If you put debugger; statements in the file (it's under toolkit/mozapps/downloads/ in the tree) they will get hit, but its content won't show properly, either.
Here are my findings, commenting https://dxr.mozilla.org/mozilla-central/source/toolkit/mozapps/downloads/nsHelperAppDlg.js#541 loads nsHelperAppDlg.js content in browser debugger
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