1) I don't have an 'insert' button either and I've never seen one in Thunderbird. But when I am writing an email in HTML format, at the top of the email composition menu there is an 'insert' menu with options to insert an image, a hyperlink, a table and so on. If you don't see that menu then you're probably composing a plain text email instead. 2) When I attach a file it appears in the 'attachments' window to the right of the to, from, subject fields. If I double-click on the file name there, it opens in the relevant program -- e.g. if it is a spreadsheet it opens in a spreadsheet, if it's a document it opens in a wordprocessor and so on. Attachments don't open in Thunderbird itself, it uses other programs for that purpose. 3) I don't understand what you mean when you say the file sometimes appears as an insert in the message rather than as an attached file. You attach e.g. a document using the 'attach' button, yet the whole text of the document appears in your outgoing message?

Thank you! Here is a better explanation for #3....

Sometimes, e-mail attachments appear below the text message, at the end of the text. They will show as images below the text, whether incoming or outgoing mail, when I wanted them just to appear in the attachment window as file names.

I don't get the "insert" menu at the top of the reply menu,

I used to have an "insert" button, on the main menu, but there is only "attach" now. I have updated the main program and maybe it is no longer an option. Still no change on the "opening attachments" problem.

Are the attachments that do display mostly images? If you have View-Attachments-Inline checked that will happen. This only happens with attachments that Thunderbird can open. Other attachments like Word docs or Excel files cannot be opened by Thunderbird so they do not display.