Fixed unnecessary extra tab from opening on Firefox

Removed reference to target_view = view.open() to prevent the new tab
from opening. Instead catching this case within the fs_error function
with an else statement, so if no target_view: window.open() and pass
the target of "_blank" to allow dataURL to open in new tab rather than
steal the current window.

FileSaver.js

@@ -94,7 +94,9 @@ var saveAs = saveAs
 					}
 					if (target_view) {
 						target_view.location.href = object_url;
-					}
+					} else {
+                        window.open(object_url, "_blank");
+                    }
 					filesaver.readyState = filesaver.DONE;
 					dispatch_all();
 				}
@@ -137,8 +139,6 @@ var saveAs = saveAs
 			}
 			if (type === force_saveable_type || webkit_req_fs) {
 				target_view = view;
-			} else {
-				target_view = view.open();
 			}
 			if (!req_fs) {
 				fs_error();