I don't see the connection between Lightning and sharing a Tbird profile between Windows 10 and Ubuntu. All you need is to store the profile folder in a location that is accessible by both OS, then configure Thunderbird in both OS to load the same profile. Are you having problems with Lightning (Calendar) in a shared profile scenario?

Sorry for the misdirection... the last time I attempted this the plugins, were an issue... In any case, let me give your suggestion a try. Does it matter that my Ubuntu is running TB78 (primary) and Win10 has TB91? Also, have any instructions for moving my TB Profile? Thanks

Yes it does matter. The versions of Thunderbird need to stay exactly the same in both OS, because once you've upgraded a profile using a newer version of Tbird (91), the same profile is not readily usable by older versions (78). You have to use the command-line switch --allow-downgrade when starting the older TB version to allow it to launch the upgraded profile.

This back and forth upgrading and downgrading of the profile does not always end well, which is why sharing a profile between Linux and Windows is NOT a good idea and I generally don't recommend doing so regardless of how convenient it might seem. If you must do it, then you must make sure that both OS are running the exact same version of TB at any given time so as to not break the profile, and even then, there is no guarantee that your add-ons (or their binary components) will be cross-compatible with the two very different platforms (Linux and Windows). You will have to experiment and confirm for yourself whether Tbird works as expected on both OS using the shared profile.

Note that this type of setup is NOT supported by Mozilla, which is probably why there is no such knowledge base article or definitive guide as you put it and there probably never will be, at least not on Mozilla Support. You assume full responsibility for keeping Tbird functional in such a scenario. You may find an article elsewhere that covers this.

Hey Hey, thanks for the replies. Sorry for "basic" questions. It has been a long time since I have had a sustained need to use my Win10 partition, let's call it "rusty jitters". In any case, I figured out the "mechanics" of it (with your help... 1.) Download / install latest version of TB on Win10 / Linux partitions 2.) from Linux partition synchronize TB Profile folder with WIn10 Profile folder, "Poof" done... I think there's no literature because all the youngsters prefer putting their whole life stories info into cloud platforms, which is something "grandpa" is just to stubborn to do. In any case, one last question and we can close this thread. If I download and install TB 91 over my current TB 78 installed via PPA, will the same ppa also take care of future updates or is it best to remove it? (can you recommend the best way to install TB 91 on ubuntu)... Thx