This is a simple bookmarklet "Firefox Notepad" source @here:
How to edit the above to open a text file instead of blank at the start?
I tried the two obvious places and they didn't seem to work; Will spaces in the path be a problem?
Sample path =
C:\Documents and Settings\Compaq_Owner\Desktop\sample text.txt
The first step would be to upload the text file to the web so that you can specify its address properly in the window.open call.