Hi, for file access, we're using JSLib "File I/O" and "Utils" libraries in our Thunderbird AddIn (http://jslib.mozdev.org/). Some of these functions utilize nsILocalFile and others, forbidden for the next major version of Thunderbird. (https://wiki.mozilla.org/Thunderbird/Add-ons_Guide_57#Removed_interfaces_in_mozilla57). Is there a new and compatible version available somewhere? The current source seems not updated since 5 years or so... Best, Volker