Anyway, assuming you're talking about Sync, I find it quite helpful for the browser so have no issues with it being extended to Thunderbird. It is, as I understand it, always optional, and I even believe it's possible to self-host it, though I haven't tried.
every once in a while I look into what it takes to self host it and never get very far. The primary problem is that it is an internal tool used by mozilla and it shows, Don't get me wrong, I think it is great that mozilla provides the code but it does not have any of the polish that a tool intended for others to use get. I am sure I could get it going if I devoted a weekend to the effort. but have not yet been willing to put that much time into it.
off my head, first you have to get the account service up and running then you can get the sync service going then you have to trick your firefox installation to use your services.
