One thing that I wonder is if I can convert my old firefox -P profiles into this new kind of profiles, and have them all be synced by firefox with a single account instead of recreating them on all my devices. On the filesystem they seem to be the same, just not in the same place.

If you are speaking of the needle position on the dial thingy, I believe it’s just the default until you vote, not meant to indicate anything (though it’s misleading). You have to vote to see actual results.