You should always use Save As to save a document to a different location to avoid dataloss in such cases. Firefox saves files that are passed to another application to the temp folder and it is not guaranteed that the file is kept after you close that application. So if you replaced the file by using save then it is likely that this has happened and the file got deleted. You can try to check if there is an undo history available in the program that you used to recover this file. If not then you would have to use an undelete utility to recover this file. *Recuva: http://www.piriform.com/recuva