Mac adds automatically a suffix when downloading a file. How to stop the Mac from doing this?

Question

I want to download a gps-file for my tomtom navigation system.
These files have the suffix .itn
When downloading, OS X transforms the file from filename.itn  to   filename.itn.txt automatically, therefore adds an ".txt", and opens the texteditor with the file.
I just want OS X to leave the file as it ist and add or do nothing to or with it. Just put it in the download-folder.
When hiding the suffix with apple-i, the file is no longer readable for the navi system. There ist no option to tell the mac just to do nothing; you just can select a different app. But this is not the solution.
What can I do?
Thanks
Mathias

Answer 1

Limnos wrote:
I use a much older version of Safari when I do use it. I have that unchcked but when I download a file Safari just downloads it without any prompt for a file name.  What the OP needs is a way to change how Safari handles downloads so it either identifies them correctly and stops adding the wrong extenion to a file, or a way to edit the file name at download time. My old version doesn't have any apparent way to configure either of these, but I can do it in Firefox.
What?
The file has a name prior to downloading, Safari does not ask for one to be added at download time (neither do other browsers), once the file has been downloaded the extension can be corrected.