edit: in reply to devs reply:
Thanks man for the reply. Oh dang ok I'll bump to 5 stars then, can you please explain how an every day guy like me can use it? I might find use for it.
That description means e.g. file:///C:/mydirectory/myproject/docs/index.html and if you look at where you can set its options you'll read "It cannot get around hard file URI scheme limitation. Also it's name is "Save Back to File from DOM", which implies it must be from a file to begin with.
This is a specialized Add-on that does something quite useful. Sorry it doesn't do what you apparently trying to do, outside its intended scope.
Excellent solution to the save problem in ff. Adding autosave would be good. A serializer issue to fix
Source code is two places, easier for me to keep track of at https://github.com/srguiwiz/save-back-xpi but tied into Mozilla's build system at https://builder.addons.mozilla.org/package/89889/latest/ My thoughts when I released it at http://leosbog.nrvr.com/2013/02/20/writing-svg-to-disk/ So if you were going to write something similar, maybe you can start from this one and modify it to your needs? Feel free to contact me to talk if not sure whether to have two different add-ons or try making it one.
cannot be installed in firefox 24.0
Had updated the code months earlier, and had thought the emails from Mozilla saying it "passed compatibility" meant everyone had access. Had to download it from one system and upload it into another system to be available for everyone. Done. Enjoy. Please change review title if you can.