I'm running Thunderbird 52.7 on Xubuntu 16.04. I made a copy of my profile, as I have done countless times in the past decade, and moved the copy to my laptop, running Xubuntu 18.04. I opened Thunderbird on the laptop, and created a new profile. I copied the contents of the desktop profile to the new laptop profile folder, replacing everything in the new with the old, and that's when the fun began. First, Thunderbird tried to open but crashed, and I got the crash notifier. Each time I tried to restart from the notifier, it crashed. Second, I deleted the new laptop profile folder and changed the ini file to the name of the old desktop folder. I got the error message saying Thunderbird couldn't find my profile even though it was there. Third, I tried starting Thunderbird in safe mode. I got an error message in the terminal detailing a memory overflow, and it wouldn't start. Fourth, I tried moving just the old mail folders to the new desktop profile, and the same thing happened. I went through each of these steps several times, deleting the .thunderbird file on the laptop, opening Thunderbird, and letting it create a new profile folder. The same thing happened every time. Does anyone have any idea what's going on? I have been doing this for years, with no problems. I always clean up my desktop mail, running compact folders, before making the copy that I'm going to move to the desktop. Plus, Thunderbird works without any problems on the desktop, so I don't think it's a corrupt folder. The only think I can think of is that there's something in 18.04 that is different from 16.04. But I'm not sophisticated enough to know what that is. Right now, I'm ready to reinstall 16.04 on the laptop and see if that solves the problem. Thanks for your help.