Consensus on the WebApps list at W3C was that we didn't want to expose this to web pages. I.e. a File should always represent a real OS-file. But we can still expose this internally of we have APIs which need to instantiate File objects and return to webpages. But I think we might already have that.
I found |new File()|, but it looks to be only callable from chrome. test_file_cross_database_copying.html should be rewritten using xul.
Ah, indeed. I think we should keep that current setup.
I have a fix for this, it's a part of the patch for bug 726593. I added a new method to nsIDOMWindowUtils (to get a file object).
fixed along with bug 726593