adapt FileSaver.js to allow including it as a content script in Firefox for Android add-ons

FileSaver.js

@@ -14,7 +14,7 @@
 /*! @source http://purl.eligrey.com/github/FileSaver.js/blob/master/FileSaver.js */
 
 var saveAs = saveAs
-  || (navigator.msSaveOrOpenBlob && navigator.msSaveOrOpenBlob.bind(navigator))
+  || (typeof navigator !== 'undefined' && navigator.msSaveOrOpenBlob && navigator.msSaveOrOpenBlob.bind(navigator))
   || (function(view) {
 	"use strict";
 	var
@@ -116,9 +116,20 @@ var saveAs = saveAs
 			}
 			if (can_use_save_link) {
 				object_url = get_object_url(blob);
+				// FF for Android has a nasty garbage collection mechanism
+				// that turns all objects that are not pure javascript into 'deadObject'
+				// this means `doc` and `save_link` are unusable and need to be recreated
+				// `view` is usable though:
+				doc = view.document;
+				save_link = doc.createElementNS("http://www.w3.org/1999/xhtml", "a");
 				save_link.href = object_url;
 				save_link.download = name;
-				click(save_link);
+				var event = doc.createEvent("MouseEvents");
+				event.initMouseEvent(
+					"click", true, false, view, 0, 0, 0, 0, 0
+					, false, false, false, false, 0, null
+				);
+				save_link.dispatchEvent(event);
 				filesaver.readyState = filesaver.DONE;
 				dispatch_all();
 				return;
@@ -213,6 +224,9 @@ var saveAs = saveAs
 
 	view.addEventListener("unload", process_deletion_queue, false);
 	return saveAs;
-}(self));
+}(typeof self !== 'undefined' ? self : typeof this !== 'undefined' && this.content ? this.content : null));
+// `self` is undefined in Firefox for Android content script context
+// while `this` is nsIContentFrameMessageManager
+// with an attribute `content` that corresponds to the window
 
 if (typeof module !== 'undefined') module.exports = saveAs;