We already sync the "block pop-up windows" prefs, but don't sync:

• "Warn you when websites try to install add-ons": this is controlled by the xpinstall.whitelist.required pref.
• "Prevent accessibility services from accessing your browser": this is the accessibility.force_disabled pref.

Syncing the add-on install warning pref could be harmful—you might set it once, then forget about it, and opens the door to a malicious site asking you to install an add-on—though the risk is mitigated with WebExtensions and add-on signing.

Syncing the accessibility services pref is more tractable, but I'm not sure if it's the right thing to do. You might have different accessibility settings per device, and, if we synced it by default, you'd need to explicitly prevent this pref from syncing via an override. We do record telemetry for how often accessibility is disabled; we can decide based on that whether to make this opt-in or out.