This issue came up in this patch: https://phabricator.services.mozilla.com/D94809?id=359957#inline-538158

If a user wants to use the ping server but also starts setting their own prefs, then the ones for the ping server might get overwritten and it would break. To overcome this issue, we should make the browser_prefs keys "write-once" and throw either an error or a warning to the user when something gets or is about to be overwritten.

We should have an option to disable this feature as well (or turn errors to warnings) in case the user knows what they are doing and aren't concerned.