The Firefox Sync add-on which Firefox 3.6 used was discontinued a few months ago and has been removed from the add-ons site.

Thank you - but that's awful. I had imagined that the 3.6 compatible addons would have been supported as long as 3.6 itself (ie, two weeks to go). Now what, please, and who takes these kind of decisions?

See:

• http://blog.mozilla.com/sumo/2011/12/09/goodbye-to-the-sync-add-on/

There are 3rd party applications that can sync between Firefox 3.6 and the latest versions of Firefox.

Xmarks can be used to sync bookmarks, history and open tabs - http://www.xmarks.com/ LastPass can be used to sync passwords - https://lastpass.com/

These are free if used with the desktop versions of Firefox, but if you want to sync with mobile devices you will have to purchase the premium versions.

Is this Firefox 3.6 on another computer? Is there a reason you can't upgrade this profile to Firefox 11? Or use the Recovering important data from an old profile to manually copy and paste your information from the old profile to your new one?

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.

You can install two versions of Firefox on the same computer, have them share the same profile, and use Sync in one (eg. Have Firefox 3.6 and Firefox 11 on the computer, sharing a profile, and have sync setup in Firefox 11). Just install Firefox 11 to a different directory on your computer (not Program Files\Mozilla firefox, maybe program Files\firefoxnew or something). It isn't supported, and you can't run both versions at the same time, but it may help with your situation.

I have already several versions of FF installed and use them in parallel - on the computer where that works. But I have found numerous problems trying to use a FF profile with different FF versions, and therefore come to strictly use one profile with one version only. As an aside, your instructions are for Windows, and I'm on various versions of Linux - but nevermind, thank you for the effort, anyway.

PS: I'm using something along the lines of

$ /path/to/firefox -no-remote -profilemanager

to start several instances and versions of FF without getting their respective profiles messed up.

Ah yes, sorry about the Linux windows mixup.

Hi Muellert2 - Tylyer's answer is really the way to go. Open Firefox 11 with your 3.6 profile and set up sync to get the info from that profile. Then you can go back to just using 3.6 on that computer. We continually switch between many different versions of Firefox with the same profile every day without issues. You can also follow the instructions in Back up and restore information in Firefox profiles first just in case.