I think this program is wonderful, both as a pixel art editor and Godot project! Something I would like to ask, though, is how you implemented the file picker.
Thank you! We used the FileDialog node. https://docs.godotengine.org/en/stable/classes/class_filedialog.html
Oh yeah, you are correct. For the Web browser we use a modified version of this addon. https://github.com/Pukkah/HTML5-File-Exchange-for-Godot