Question: I know the question has been asked thousands of times, but I'll ask it again: is there a way (even patchy) to write/read a dumb text file with Javascript or Protoype ?

This is only for debug purposes, and is not designed for production. The thing is I need it to work with (at least) both Firefox and IE (preferably under Windows).

Thanks in advance !

Answer: 
Writing to a file is not possible, you'd have to write a server-side script and make a request to that script. Reading is possible if you use an iframe with the text file's location as source, and reading the iframe contents.
Only with a server side javascript interpreter, but that isn't the typical environment you run javascript in.