Hi nauna,
TinyMCE has paste_data_images setting which allows you to paste images in the editor. This is false by default. So you will need to set paste_data_images: true in your init file.
Firefox allows pasting of images in any contentEditable field so you are able to paste in FF.
You can refer to documentation for more information
https://www.tinymce.com/docs/plugins/paste/#paste_data_images