Were you having issues with messages on IMAP having corrupt attachments? If not you probably don't need 50.5.1

Having said that, a full install is only slightly larger and does not involve any re setting up. It just replaces the program stuff, not the settings or data.

I had no problems, but I generally like to keep up-to-date (I presume the 50.5.1 was a typo - should be 60.5.1). About a full install: I have an add-on that allows TB to interact with an Office365 Exchange server (the ExQuilla add-on) that was a pain to set up to work properly with my institution's settings (not the add-on's fault). If I download and do a install, will I need to start over with the add-on and its settings again. Or is there a way to incorporate existing add-ons into a full install? THANKS

Update - today the TB update to 60.5.1 worked, without any other action on my part - did not restart computer or the program (which I had done previously to try to get it to work, but without success). I have no idea why it suddenly worked. So this "problem" is solved - but I would still be curious to know about the question posted above about add-ons, should at some point in the future I need to do a full install. Thanks

Add-ons and add-on settings are stored in the profile folder, along with your account settings, mail, calendars, address books etc. The profile folder is separate and not affected by the uninstall or reinstall of the TB program, although in some cases an add-on may need to be updated when TB is updated (or downgraded). For backup purposes, back up the Thunderbird folder, the folder that contains the Profiles folder (which contains the profile folders). That is the easiest way to restore a TB setup or transfer it to another computer.

Thank you so much for this - my add-ons have survived many updates so I suspect I will have no problems. Update problem solved (for unknown reasons) and new information gained. Thanks again.