use tags for marking messages because tabs will never be reliable. They can not be.

BTW the most common cause of coming back to closed programs is a windows crash. With Windows 7 and later, a blue screen of death quietly reboots your computer so you do not know the operating system is crashing regularly. This is particularly not noticeable if your have no operating system password to clue you in that your being asked for the startup password. Clever marketing is what it is.

Thank you, Matt. I will do as you say. I didn't know about Tags until this very moment. Even if I had, I wouldn't have thought to use them as "tab insurance". Thanks again.

When you say tabs will never be reliable are you also talking about Firefox or just Thunderbird? I haven't lost my tabs in Firefox for a couple of years now so have I just been lucky or is Firefox stable? Or does stability come and go with various updates?

Bottom line is tabs live in a file called session.json. All sorts of privacy and "speedup" type tools delete this cached information. One of the really popular ones is CCleaner. In the case of Firefox they have an additional backups they can restore from, but it is only a matter of time before these same tools. but in the case of Thunderbird functionality is somewhat reduced. Manly I think because no one at the time thought people would come to rely on tabs. In the underlying code tabs are messy and really large parts of the "vision" await further attention. Thunderbird in reality only has one and the rest is smoke and mirrors hence my particular issues re reliability long term. Compose in a tab may see more work done on the tab part of the interface to make it more robust.

Having said that I have had issues with Firefox in the very recent past, but I also run nightly builds so expect issues most people never see. (Testing comes in many forms.)

Making your own backup of the session.json file is a workaround if you feel strongly enough, but personally I think saved search folders and tags are a much improved arrangement as most IMAP servers support them so your tags appear on your other devices as well.

My view is. Tag mail as say "To do" open find Ctrl+Shift+F set a search criteria for tags contain "to do" set the folder and sub folder to search click search to make sure your criteria is working and then click save as search folder. Thunderbird now has a new folder which only contains your "to do" tagged mails. Search folders are a vastly under utilises feature (probably because no one knows they exist) but they make a lot of business type functions much easier. (they are what underlies the "unified" folder view {View menu > folders > unified} a collection of search folders.

"Mark it as solved" button gave me an error so I had to click on "This doesn't solve my problem" to get back here.

But this does solve my problem and I want to thank you for taking the time to be patient to explain all of this to an old codger.

I don't have time to try everything you suggested right now so I have tagged the email with the To Do tag as a reminder for later.

Thanks again, Matt. Regards, Bill