How to stop Firefox from opening downloaded files automatically

Open Settings from the Firefox menu on your computer. Look for Files and applications on the Downloads page, or Applications under General if your version uses that layout. Find the content type that is opening, then change the action to Save File or Always ask. For example, change the spreadsheet entry if downloading a spreadsheet launches a desktop app. Leave other file types alone if they already behave as you want.

In the Downloads panel, right-click a recent example to see whether Always Open Similar Files is enabled. That option uses the system default app for similar downloads. Test with a fresh download of a trusted file of the same kind. If a file from one site behaves differently from the same kind of file elsewhere, the site may be reporting a different content type. Firefox uses what the site sends, so the extension alone is not enough to identify the setting.

If the file stays closed but the Downloads panel appears below the toolbar, right-click the Downloads button and turn off Show Panel When Download Begins. You can still open the panel manually to find your downloads. This setting changes the panel behavior; it does not change the action Firefox takes for a particular file type.