I've read that there is an add-on that adds Sync, included with FF starting with 4.0, to Firefox 3.6, but can't seem to find it. I'd like to use it to merge my 3.6 stuff into my FF11 profile...

Question

I've read that there is an add-on that adds Sync, included with FF starting with 4.0, to Firefox 3.6, but can't seem to find it. I need to keep a zoo of different browser versions, including 3.x, but want to sync stuff nonetheless.
So far, I tried variants of "Weave" and "Sync" on addons.m.o, and Google, but to no avail.

Answer 1

I use several different computers, different software, and a mobile device, too. I have the bulk of my important data in a FF3.6 profile, and I also need to keep the FF3.6 for web development purposes (every version renders slightly different, but the difference between 3.6 and 11 is very noticable). Also, FF11 has some problems, like forgetting passwords, but accrued an independent set of bookmarks, passwords, add-ons etc., so trashing that is not an option, either (although I am usually on 11 these days). Wading through tons of stuff to merge is not a good option either, and Sync would have helped to unify all of that.
@TonyE: Would Xmarks and LastPass merge with Sync data from newer FF? I'll give that a whirl.
@cor-el: Thank you for the link. It does explain the current situation, but the arguments put forward in that article are that highly aggravating marketing speak that I have come to expect from the Mozilla Corp. guys.
I still don't understand why they couldn't let the addon online for a few more days, maybe with a disclaimer that support ran out on mm/dd/yyyy, and that it will e.g. be pulled together with the main product.
@Tylerdowner: I'll probably try to merge the stuff from 3.6 into 11 by creating another FF11 profile and then use Sync between them.
@all: Thank you so far. If someone has a pointer for where to get eg. the source code of the pulled Sync, I'd highly appreciate that, too.