Changed isp and email completely, and wanted to change both server name and user name.

Don't mess with your existing account. Create a new account in Thunderbird for the new server with the new credentials. Make sure to give it a unique name.

Thanks for your tips, but that is an awful lot of work compared to what I did even. - checkboxes here and there - a lot of text to fill in - remove and account and have old maildatabase left - assign new account to same database

I only had to change domain on three places, mail was the same.

I think looking through how lost focus on fields work instead. - I did plenty pre- and post-processing on focus() event and it can be done better. - just set a flag if leaving a field is changed - and process which changed fields as you get focus() on other fields below - then execute restart thingy

Just how I would do it...

I have almost 20 years of emails on 6 accounts in this install. So want minimum work changing ISP. New accounts will be used as continued same account as previous keep same history data.

It's up to you to follow suggestions or not. Good luck.

Yes, and it's up to devs to listen to good advice, too! - this is what feeds donations coming - troublefree functionality

It's simple programming task to solve this in no time. - I'm a retired programmer and did this many times as I described - simple overlooked thing that can be fixed

I went through as is now, and solved for me. - this was for other peoples future needs - not for me right now, but in future next time I change ISP

Not sure how you report to devs anything, that might be a thing to solve with a bug tracker.

Not sure how you report to devs anything, that might be a thing to solve with a bug tracker.

You can raise a bug in Bugzilla. https://bugzilla.mozilla.org/