[yoklov]

Being a global persisted key value store, about:config has a lot of things stored in it that.... do not necessarily make sense syncing, hence it being opt-in. Sync is guilty of this too, and will store things like your last sync time in about config, for example. Clearly not meaningful to sync directly.

A checkbox like you describe was actually discussed in the past, but at this point it’s unlikely. The current design of letting any synced machine change any pref on any remote machine (effectively) has dubious security implications, and has gained an additional hoop you must jump through in nightly.