I use quotecollapse addon.

Wayne Mery said

I use quotecollapse addon.

I looked at quotecollapse on its home page at http://mjg.github.io/QuoteCollapse/ . I don't understand what that add-on does, but I'm fairly certain that is not what I was looking for.

To clarify, when replying to an email, and wanting to quote the original message, which generally appears below the reply portion, and there is a series of replies (all quoted messages), the quoted sections are identified by multiple levels of quote marks, such as blue vertical lines along the left side of the quoted text. Sometimes I need to add those quotes levels to such text, or remove some of those quote levels, based upon what the other people have done (or failed to do) when replying to that thread of messages.

In Eudora, it had on its Edit menu a Text choice, where you could add a quote level or remove a quote level. That's what I want to do in Thunderbird.

The only thing similar to this in Thunderbird, in a Compose window, is on its Edit menu, which has a Paste As Quotation choice, but that only adds at most one quote level (not multiple levels) and doesn't offer a means to remove one quote level.

I don't know of such an addon, but there are feature requests in bug reports https://mzl.la/2JrLWKD

Wayne Mery said

I don't know of such an addon, but there are feature requests in bug reports https://mzl.la/2JrLWKD

Thanks for researching this issue. Of the four bug reports listed in the link you provided, the second one, Bug 298576, is exactly the problem I would like resolved. Since that report is several years old (from 2011) and this issue hasn't yet been remedied, I expect it won't be.