Stopping a download by clicking the “Abort” button is currently not possible as this feature is not yet implemented in the yt-dlp API. Instead, only subsequent downloads in a list of URLs can be stopped.
Drag-and-drop of text and URLs not working with Firefox under Linux. Using a web browser other than Firefox or dragging and dropping text from a text editor seems to work fine. Please note that this issue is related to Videomass v4.0.11 and affect Linux OS only.