Formatting paragraphs / embed images within Richedit fields content is not possible if one is using Microsoft Edge
The issue seems related to this so called browser not fully supporting outline-offset spec.

Steps to reproduce:

• Using Microsoft Edge, on a clean installation of eZPlatform, edit default Welcome to eZ Platform content object.
• Click somewhere within the Short description field content.
  => The toolbar that should allow you to format the paragraph is not displayed.
• Click somewhere within the text "eZ Platform (and eZ Studio)" right to User Manual link
  => The toolbar that should allow you to format the paragraph is still not displayed.
• Click on "User Manual" link.
  => A toolbar to redefine the link is displayed and it's coordinates will be used for the toolbar, when you click next on any paragraph, within this field.