In Firefox 91, files opened after downloading in external applications will be automatically saved in the standard "Downloads" directory instead of the temporary folder. It should be noted that Firefox offers two download modes — save and open in an application. In the latter case, the downloaded file was saved in a temporary folder that was deleted after the session ended.
This behavior frustrated users who, when needing direct access to a file, had to search for the temporary folder where the file was saved, or re-download the data if the file had already been automatically deleted. It has now been decided to save files opened in applications similarly to regular downloads, which will greatly simplify operations like sending a document to another user after it was initially opened in an office suite or copying a multimedia file to an archive after opening it in a media player. Chrome has implemented similar behavior from the start.
Source: opennet.ru
