I have deported my thunderbird profile on a folder that is syncing with a server (like dropbox). My two computers, under linux and under windows, are connected to this synced folder with the Thunderbird folder So, when I read a message in thunderbird, it appear readded to on the second computer. It works perfectly !

What is not working, is the calendar plugin (lightning). It must be the same for all plugins. It seems plugin for windows and for linux are not the same files. So, When I connect Windows, plugin ok, then I connect Linux, plugin is disabled. I need uninstall under linux and reinstall plugin to make it work. But after that, plugin is disabled under windows, I need uninstall and reinstall under windows. So it is disbaled under linux ... and so and so ... . The fact, is plugins are stored in an unique folder. Soluce could be store plugins for windows in a folder named "Windows" and plugins for linux in a folder "Linux". So it should work perfectly. An idea to explore.