Well, the "ship has sailed" for adding a secondary email address to your current Sync / Firefox Account. And trying to get someone on a weekend to help you would be difficult to impossible. Plus that "I have create my firefox sync account long ago" doesn't bode well.

Might be easiest to just create a new Firefox Account with the email address that you would like to use - with the original device which you were using with the current Sync / Firefox Account. That will get your existing data into the new Sync / Firefox Account; then it's just a matter of connecting the new devices to the new Sync / Firefox Account.

Thanks Edmeister, but "create" doesn't mean "haven't use": I'm still using it to sync extensions, bookmarks, history and so on between my desktop, my notebook and my mobile daily. So no, creating a new one doesn't sound good for me. And I'm asking you today, because on the week end I have some spare time to use to configure my PCs. I don't think that this should be posted on a forum: this isn't a problem/bug, but a "feature" of the developers implemented for I don't know which reasons. Last, I haven't add a second email because, last time I tried to change it, it wasn't possible.

Sorry, but due to a recently added features to the Firefox Accounts system that has to do with "verification" and the secondary email address you are now "between a rock and a hard place" with a locked Firefox Account log in process. And that needs the help of Mozilla staff which typically don't visit this forum even during the week, but are usually available for contact by a moderator during week day during work hours, which vary around the globe. Now all you can hope for is a staff member wandering in here during their time off, which does happen on occasion but something to be counted on. Now that I said that, you may get lucky".

As far as creating a new Firefox Account, if you desktop device is not one of the "new devices" you mention - IOW has all your Firefox data - all you would be missing would be "mobile" extensions, so creating a new Firefox Account wouldn't really affect you.

And no, "changing" the email address just has never been possible, it is the primary identification for the account; that is why a secondary email address feature was added. I have had to create 3 different new Sync accounts / Firefox Accounts over the years as I tried to get away from spam."

Ok, thanks for you deep reply. I will wait some days and see what will happen. If no one from the staff contact me in this time window, I will move to a new account. (Also: is it possible that for such problem you HAVE TO contact a staff member, but there is NO WAY to do so directly?)

It seems that somebody read this post, because today I was able to send a new mail to verify my account, so now I could sync it on all my PCs