It may help if you post a screenshot of what you see.

Sure. Let me see if I can figure out how. Note that this applies to the appearance of incoming mail only. My new messages, of course, do not have either the mail toolbar or this strange new duplicate.

I don't see the image, and it did seem to hang on "uploading," so let me try yet again.

I don't see anything unusual in the screenshot. Please share some of the text in that line, so I'll know which one you're concerned with. Thanks.

You can't be serious. It's not that hard to describe, and I've already done so. (Besides, you can always click on the image to enlarge it and see clearly anything I might try to type.) But here goes again: there are now two toolbars with all but the same commands and functions. Look! One at top left, right below the menu bar, has no text and the image style I prefer. I can turn it on and off, but would rather have it on. And, as of 48 hours ago, there is now below that and to the right a second mail toolbar (with text and images) that I can't figure out how to turn off, and I have no idea what turned it on.

That toolbar in message view has always been there.

I mean to be helpful. I attached several old screenprints from the internet of Thunderbird, all showing the toolbar on the right. If I'm missing something, please clarify.

Now wait a minute: that's just not true. All three show only one, not two mail toolbars, and all have it on the left with in one case the ordinary menu bar, just as I'd expect. But looks like my only choice is to kill the mail toolbar and live with the new toolbar that can't be customized (at right). In fact, if I go into view options, toolbars, and click on customize, the selected changes (such as whether to add text options or other icons) affect ONLY what I think of as the ordinary mail toolbar at left.

And no, I'm not saying that I never had a mail toolbar before! I'm saying that I never had a dupe toolbar and, too boot, one I can't control.

Just to be sure I know which toolbar you are concerned with, I marked it on the attached. My guess on your seeing duplicate content on toolbars is that the other one can be customized by user. I also have a large toolbar with reply, forward, etc and that is above the other one, which sits on top of the message pane.

May I try again? This time I've annotated a screen shot. I don't know why it's so hard to follow my question, but I'm trying my best, honest!

Okay, here's an update. I have a friend who is a super Thunderbird guru and used to be a project leader there. There once was such a capability that was removed and the feature is not there today, but there is an active bug that is being researched to put back in on a future release. So, you aren't crazy, in thinking this used to be an option. I spent extra time on this because you were so passionate about this - and you were proved right. I have no idea when it will be released, but here is the bug report: https://bugzilla.mozilla.org/show_bug.cgi?id=1773314 go pour a beer and celebrate your sanity.  :)

Thanks for all the work. You're a bit over my head here, but I'll take your word I'm not losing it, and we'll see what happens. For me, the bug is quite new (as of two days). How curious that the visible toolbars don't entirely match up with the menu choices!

I have not tested it for current version of TB, but there is an addon, message header toolbar customize. I don't know if it addresses your needs exactly, but it's worth a shot. Good luck.

Thank you. I'll check it out. (And now I have a name for the second toolbar, not Mail Toolbar but Message Header Toolbar. That could prove useful at some point, too, even if doesn't appear in the menus.)

For what it's worth, I still experience the problem. Let me give more detail.

On opening Thunderbird, I see the menu bar and, just beneath it, the mail toolbar. The latter is icons only, and both the menu bar and the mail toolbar can be removed using View, Toolbars, and unchecking. (Not that I'd like either of them to go away!)

On starting a message, I see something similar, although instead of the mail toolbar, it's the composition toolbar. Again its at left and icons only, and it too can be removed (although I won't) with View, Toolbars.

However, on opening a message in my inbox, I have the TWO mail toolbars. The one at left, the desirable one and the one consistent with those other views I just described, can be removed with View, Toolbars. However, there's the second one. Unlike the others, (1) it's at right, (2) it consists of raised rectangle buttons with text and an image (a look I don't care for), and (3) it isn't among the options in View, Toolbars. Surely Mozilla can't intend this, or it wouldn't have allowed us to remove all those other toolbars (not to mention the status bar)! And it wouldn't have styled all the others differently.