Is there is list of file formats that have changed, and with which versions?
Before COVID, I would travel about once a year. I would just copy the profile from my office email machine to my laptop, set the desktop computer to stop downloading emails (the laptop was always set to leave them on the server), and go traveling. When I returned and turned my regular email machine back on, turn the "leave on server" off, and download all the emails to it.
The COVID break from traveling meant that some file formats had changed. When I tried to load the v78 profile from my desktop to v68 on the laptop, I got a lot of errors, and went on to do other chores. Now I've come back to this issue and decided to just load v 102 to my laptop. I want to be able to load all those emails and the address book. Does v 102 read earlier versions of files, and which ones? I have a large volume of emails that I want to load, review, and then archive about 99% of them. I really need to retrieve the address books, get rid of duplicates and dead addresses, and then save about 85% of them a vcards before deleting them from the address book.
It would really help to have a list of the files that changed with each version, so that we can see what files we need to look for.
I'm hoping that 102 will convert all previous formats, and if not, I can have a list so I can migrate these v 68 files to 102 when it imports them.
Running Win10 21H1.
Is this about downloading emails in Thunderbird ? In that case we can move the thread to Thunderbird support.
You can't downgrade a profile like you did safely, you can always expect issues as this isn't supported.
Can't you upgrade the device with Firefox 68 to a more recent Firefox version ?