Tools>options>privacy&security>Passwords. Click 'show passwords' and then right-click on the account to change.

Not exactly what I had to do, but still helpful. Password Manager wasn't under tools at all, but preferences was its own choice and I found it under that. Sorry I've taken so long to reply----have had so many misadventures lately.

In Thunderbird 91.8.1 I found the solution under

Tools -> Preferences -> Privacy and Security in the Passwords section.

Here you can view passwords for each email account and remove them if required.

Hi Mike - did you read what I wrote above? Mine was NOT under tools - but I did find it under preferences. Thanks for trying to help, though.

Hi Stellawrites Maybe you have a different configuration of Thunderbird than me, as I have the Menu Bar turned on as I find it useful, and the Preferences are definitely listed under Tools. You can of course also get directly to Preferences through the 3-line Thunderbird menu. What threw me originally was that there is that Options is not listed under the Tools menu.

Y'all keep forgetting that Thunderbird is the most popular email client for LINUX operating systems... not just Windows and the Big Mac. When running Ubuntu/Linux version 20, with Thunderbird 91.8.1 it turns out you can find the mysterious disappearing Password Manager this way:

1) Turn on the Top Menu Bar. The top menu bar is your friend when all else fails and has been forever, especially with LINUX. But you can also click the hamburger icon at the far upper right of the Tbird home page if you must.

2) In the Top Menu Bar click on "Edit" and then click on "Preferences" in the drop down menu.

2(a) For hamburger fans, you find "Preferences" in the middle of its list and click on it.

3) Either way, you are now on the preferences/settings page. Click on "Privacy & Security" from the left hand column

4) Look in the middle of the "Privacy & Security" section for the "Passwords" heading. Now look to the very far right on the screen and you should see a small white box that says "Saved Passwords..." it is easy to miss and it does NOT look like a clickable button, but it is. Click on it and Bingo: You are in the password manager.

Now, wasn't that simple... intuitive, huh? uh...Not Really. Certainly not as intuitive as it was before Tbird was "improved" to be more like Firefox (...don't' get me started...) Before that, all you had to do was click on "Tools" and then "Options" and finally on "Passwords". You didn't hardly have to move the mouse pointer at all. Hey, did I miss the memo? When did "refined and polished" become synonymous with "more complex and time-consuming and harder to remember where something is the next time you need it"?