I wonder if they’re using my data to something or spying on me.
Because I use Firefox Sync to sync mostly my history. I don’t have bookmarks, I just remember what site I want to access by its URL then I start typing and the autocomplete do the rest.
For example, to access Lemmy I just type “le” because the only site I most access and starts with “le” is “lemmy.world”. Rarely I get some conflict on this approach. And it works on both my phone and desktop.
I wonder if should I change this approach to avoid Firefox Sync or I can trust on Firefox Sync.


my point is that all terms and conditions are subject to change without prior notice to you and your continued use of the product and or service is agreement of the terms that can, and will change
That would be a violation of EU law. You cannot change such agreements without notice.
You are not wrong but at that point it applies to any and all services out there. Companies typically send an email notifying the change in their TOS and post it in their blog/website. Depending on the change I’ve seen that they even say that users have a deadline to react accordingly. Firefox has its controversies but I have no reasonable suspicion that they will pull that risky move of spying on that encrypted sync process and go against their whole mission and user base.