I am also trying cmd.exe output each oSession.url to > somefile.txt.
If you are merely trying to scrape the MP3 urls into a file for some later use, then the idea of outputting them to somefile.txt
seems simpler than trying to interact with Excel from FiddlerScript.
Add the following line (to your code), which accomplishes appending the latest MP3 url to somefile.txt
(note: I placed my text file in a particular folder):
System.Diagnostics.Process.Start("cmd.exe", "/c echo " + oSession.url + " >> c:\\temp\\somefile.txt")
The file will accumulate the MP3 urls as you click. Hope that helps.