There are several preferences used by the Download Manager. This article provides a list of them.

Preference Description

browser.download.antivirus.dontclean

Note: in Gecko 1.9.1.
A boolean value that indicates whether the anti virus software should try to clean a downloaded file when a virus is detected.
Default value is false.
browser.download.manager.addToRecentDocs A boolean value that indicates whether or not new downloads should be added to the recent documents list.
Default value is true.
browser.download.manager.alertOnEXEOpen A boolean value that indicates whether the UI Should alert the user about the dangers of opening (executing) an EXE. The user may check a "don't ask" box on the UI to toggle this.
Default value is true.
browser.download.manager.closeWhenDone A boolean value indicating whether or not the Downloads window should close automatically when downloads are completed.
In Thunderbird the default value is true.
In Other Applications the default value is false.
browser.download.manager.flashCount Indicates the number of times the appropriate user interface element should be "flashed" to get the user's attention when a download completes.
Default value is 2.
browser.download.manager.focusWhenStarting A boolean value that indicates whether or not to focus the Download Manager window when a download begins.
In Firefox,Thunderbird and SeaMonkey the default value is false.
In Other Applications the default value is true.
browser.download.manager.quitBehavior Indicates what should happen to in-progress downloads if the application is quit while they're ongoing. 0 indicates that the downloads should be paused and resumed automatically the next time Firefox is run; 1 indicates that the downloads should be paused but will not automatically resume when the application is restarted; and 2 indicates that the downloads will be canceled on quit.
Default value is 0 (resume on next launch).
browser.download.manager.resumeOnWakeDelay An integer value indicating the number of milliseconds to wait after the system wakes up from sleep before resuming downloads.  Default value is 10000.
browser.download.manager.retention Indicates how long downloads are retained in the Download Manager's queue after the download is completed successfully. 0 indicates that the download should be removed upon completion; 1 indicates that completed and canceled downloads should be removed on quit; 2 indicates that downloads should never be removed automatically.
In Firefox and SeaMonkey the default value is 2.
In Thunderbird the default value is 1;
If the preference is missing, the value 0 is used.
browser.download.manager.scanWhenDone A boolean value that indicates whether or not to perform virus scans after downloads are complete. On Windows XP SP2 and Windows Vista, this value also indicates whether downloaded files trigger a security warning upon launch.
Default value is true.
browser.download.manager.showAlertInterval The minimum number of milliseconds that must elapse between download complete alerts; if two downloads complete within this amount of time, only one alert is displayed.
Default value is 2000 (2 seconds).
browser.download.manager.showAlertOnComplete A boolean value that indicates whether or not an alert should be shown when downloads complete.
Default value is true.
browser.download.manager.showWhenStarting A boolean value that indicates whether or not to show the Downloads window when a download begins.
The default value is true.

browser.download.manager.useWindow

Note: in Gecko 1.9.1 in bug 439495
A boolean value indicating whether or not to use the Downloads window (true) or display download status in the status bar (false) in the browser window.
Default value is true.
browser.download.useDownloadDir A boolean value that indicates whether or not the user's preference is to automatically save files into the download directory. If this value is false, the user is asked what to do.
In Thunderbird and SeaMonkey the default is false.
In Other Applications the default is true.
browser.helperApps.deleteTempFileOnExit A boolean value that indicates whether or not to delete the temporary file used by the Download Manager after the download is complete.
On Mac the default value is false.
On Other OSes the default value is true

If a preference is not set when the Download Manager looks it up, the Download Manager assumes the default value but doesn't necessarily add the missing preference. The following table however, includes preferences which must be included in any product for the download manager to function.

Preference Description
browser.download.dir A local folder the user may have selected for downloaded files to be saved. Migration of other browser settings may also set this path. This folder is enabled when browser.download.folderList equals 2.
browser.download.folderList

Indicates the default folder to download a file to. 0 indicates the Desktop; 1 indicates the systems default downloads location; 2 indicates a custom (see: browser.download.dir) folder.

In Firefox 3 and earlier, the default is 0 (except on Windows Vista, where it's toggled to 1 on initial launch). In Firefox 3.5 and SeaMonkey, the default is 1 on all platforms.

For Thunderbird, the default is 0.

See also