Did you remove bookmark 1 and 2 before connecting to #2 and did you remove bookmark 3 after you logged out from #2?

You do not lose most data downloaded from Sync once you disconnect a device (tabs expire), so the only thing that will happen is that you Sync bookmark 1 and 2 to #2 and bookmark 3 to #1 if you reconnect to an account and do not cleanup old synced data. So basically both Sync accounts eventually get the same bookmarks (you can't set the sync direction).

you can't set the sync direction you broke my heart... How this is not possible? I just showed an example, but obviously I want to have like 30 different bookmarks in each account. One account is for work, the other for my personal use, and I don't want to mix them. If I have to erase my data when I login and logout, doesn't make sense at all.

I thing Google got it right: - Once you log-in to your Google Sync account, it get all data from your account override the actual data of my browser. While I'm logged-in, all new changes are stored in my Google Sync account. - If I log-out and log-in with a different account, its like, first it is erasing all my browser's data and then imports my Google Sync data. It's like a new browser, with all my customized data.

If you tell me that FIrefox Sync doesn't work like this, I will give you many thanks for solving my question and also I would know where is the right place to tell Mozilla that, in my opinion, Firefox Sync needs an improvement.

does Mozilla NOT have a solution for this problem. Do they even care?

What solution are you looking for?

Overall, Firefox Sync just doesn't work as the OP of this thread wishes it to work. And with this OP attempting to compare how Google Sync works to how Firefox Sync works, it just confuses things.

I found a solution in another thread. thanks