Unfortunately these features cannot be implemented due to API limitations.
1. Not possible. Firefox sets the length of the string. Also there is a Firefox bug where the ".." is appended in all situations.
2. The main menu icon is always the add-on icon. Eventually you can suggest a nicer icon for the add-on.
3. Again this is not possible by using the context menu. It could be implemented in a different way by opening a small window after clicking in the context menu or after the text is selected. But I think this way will be more inconvenient.