* Added support for private windows
* URLs saved from private windows will now also be reopened from private windows
* Behind the scenes refactoring

* When saving URLs from multiple windows, they will be stored in separate keys in JSON file
* When loading JSON file with multiple keys, each key will open new window. The list of URLs will be opened in their respective windows.
* When no filename is specified in advanced mode, default filename is used.
* Illegal URLs such as "about:debugging#/runtime/this-firefox" will be skipped.

* It is now possible to select to keep the date-prefix or not
* It is now possible to save tabs from current window only or all windows
* It is now possible to give custom name to the downloaded JSON file
* Updated icons