You need to contact ESET support if no one answers your question. Note: If you change the password for a website, the Password Manager should ask if you want to save the new one.

Thanks, but I already contacted ESET customer service. They were dismissive and claimed it is a Firefox problem. We'll see if anyone else has any suggestions for me. Again, thank you.

Does it work better if you disable auto-fill and instead use "Use Saved Login/Password" in the right-click context menu ?

No, there is no difference if I disable the autofill. ESET opens a new browser window to give access the bank's logon screen and my old password is still there and prefilled.

That could be the form filler built into Firefox. Click in the field, enter a character or two and STOP ! Using the arrow keys, highlight an unwanted entry. Then press Shift > Delete

Repeat as needed.

I can't highlight an unwanted entry with the arrow keys, only with the mouse.

When I enter the URL for my bank, ESET opens a new Firefox browser. But the opening page also has a message welcoming me to the new Firefox and asking me to set a theme. If I either set a theme or select "Not now" I then am taken to the logon page for my bank account. When I look at the settings for that new browser that is opened, my old password appears, even though I have deleted that old password from the regular Firefox settings. In the new window, I can reset or correct that password and then proceed. However that corrected setting will not be saved for my next session. Is this Firefox or ESET, ESET says it is Firefox and I don't know who is correct.

Update ESET. If the problem continues, disable it.

Thanks for your efforts. The problem has been resolved by clearing my Firefox history and cache.

That was very good work. Well Done. Please flag your last post as Solved Problem as this can help others with similar problems. Go to that post and click the 'Solved' button to its right.