Basically I am using mull on android and librewolf on linux.I want to use firefox sync or something line that for syncing.So how good Firefox sync is, in privacy point on view. I am not anonymity paranoid I just want privacy so basically what do they collect and for what?
Technical point: US companies still need to abide by the GDPR when the user is in the EU or UK.
(But yes, I accept your main point - that protection is not shared to US citizens of those same companies who operate two very different levels of distinction. European originating software/services usually operate at the higher level of protection across all users. )