how can I reset the mime-type of .tmp files in my file browser?
 

My file browser (Mate Caja) used to show me which of the .tmp files in my browser cache were video files (or any other type). Then I changed the default application for opening .tmp files, and now the file browser always says that the type of any .tmp file is 'tmp document' instead of looking at the content of the file to see if it is a video file or whatever.

So does anyone know what I should do so that the file browser recognises the correct MIME type (video/x-flv and not application/x-extension-tmp)? I'm using Arch Linux with the Mate Desktop Environment. Thanks.