Download and save file inside my extension folder in Firefox?

I would like to do the following from my firefox addon:

a). Determine my addons folder location.

b). Prompt the user to initiate a download.

c). Download and save the download

All the code examples available are for older API's and I have no clue on how to get them working for recent E10 (multi-process) code changes.

Solution

A - Get addons folder location

var OSPath_addons = Services.dirsvc.get('XREUSysExt', Ci.nsIFile).path