How works Firefox Sync?

Hi,
I would like to know how Sync works.

Is it only a synchronization tool or is it also a backup tool?

How can I be sure that no data will be overwritten? For example, I have a PC1 on which I have 100 bookmarks. I have a PC2 without any bookmarks that I have just installed and I want to synchronize it with PC1; how can I be sure that I will have the 100 bookmarks on PC2 and not, on the contrary, that during the synchronization I will end up with no bookmarks on PC1?
Basically, is there a synchronization direction, a kind of reference profile to ensure that data is not overwritten?
Thanks for your light! :slightly_smiling_face:

Anyone who knows Sync and could explain how it works?

https://support.mozilla.org/en-US/kb/how-do-i-set-sync-my-computer answers at least one of your questions.

I’d also like to better understand this.

If you don’t get an answer here, you might have better luck at https://support.mozilla.org/en-US/questions/new/desktop