browser.download.lastDir.savePerSite controls whether the directory preselected in the file picker for saving a file download is being remembered on a per-website (host) base. If set to
true, the data is stored as content preference.
The last used directory for the website (host) serving the file for download will be preselected in the file picker. If no download directory for the current website has been stored,
browser.download.lastDirwill be used.
The last used directory for any download (stored in
browser.download.lastDir) will be the preselected directory in the file picker.