I've heard this is possible, http://texturizer.net/thunderbird/share_mail.html but it's not obvious how to do it, and it only works for sharing the mail data. I think it would be awesome if Thunderbird could make it possible to /easily/ share an entire profile (including the prefs, mail filters, *addressbook* etc.) across OSes. (You could probably dominate the Win/Linux dual-boot market with this. Not a really big market, but sharing mail that simply would probably make it bigger.) I tried to share mail with Mozilla once, but although the mail files themselves were available to both OSes, some other critical files weren't -- like the "these are the messages we've already downloaded from the POP server so don't download again" data. I could read and send from Linux just fine, but I'd have to reboot to Windows to check/download new mail if I didn't want to screw up my inbox.
Related to Core bug 58647?
apparently according to bug 298265 it's possible but not terribly functional (doesn't share 'read/unread' marker properly)
David, iirc you told me this type of issue is essentially wontfix?
it's basically not supported, right. People do it, however. I didn't know that popstate.dat doesn't work across windows/linux - that surprises me a little.