i can download files and see the preview but when they are complete the icon of the file type dissappears and i cant open the file

Go to Limewir>tools>options>saving>save folder to check where your downloads are going. Go to that folder, find the file and double click the file and it should open in your default player. If not right click and chose another player. VLC player is good for awkward video files and might be your answer http://www.videolan.org/vlc/

I'm not sure if I understood the question correctly but let us know if you need more help

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To get Phex Click on the Fox