I think that uploading bookmarks to the computer of other guy (server) is not private or save thing to do. There are a lot of laws which may force to open that data about you and a lot of ways to bypass cryptography/security exist, as computer is not small and simple system.
Firefox Sync is end-to-end-encrypted, meaning your data gets encrypted before upload and decrypted after download. The encryption key, i.e. your password, never leaves your computer. The way a password reset works, is by simply erasing your data from the server and then re-uploading from your Firefoxes. This means, if law enforcement or attackers get data from Mozilla's servers, they can't do anything with your Sync data.
I'm on board with being sceptical about security, but this is one of the simplest and most bulletproof approaches.
agree, but still backdoors sometimes leak to the internet. The companies who store data centralised like messeges usually have a big legal pressure like Telegram while it had system Ton. Idk if Mozilla have that sort of pressure, I would not question it if it would be decentralised system. Anyway there are always compromises and it souldn't be too much focus on it. For example basically all programming languages are have closed source parts, simply because CPU scheme is usually proprietary and could not be checked after manufacture.
programming language -> .... -> programming language -> assembler -> CPU scheme
Without trying to sound condescending, you're basically rambling surface level half-truths about encryption, companies, legal pressure and proprietary components like IME.
Firefox Sync is open source. It gets encrypted locally. If for some reason someone is interested in your bookmarks, they won't be able to get them from a Firefox Server. They'll simply grab them from your local system in their unencrypted state.
Yes, most currently relevant CPUs for consumers, implement something like the IME or the AMD equivalent of it. This can be a source of paranoia, but, unless you are expecting to be the target of state actors, not a very logical one.
It honestly sounds like you read some technical keywords, looked up their definition on Wikipedia and drew your own, wrong conclusions.