Move network.proxy.failover_direct=false pref to base-browser

network.proxy.failover_direct: we set it (to false) but only for TBB, we should see if it makes sense to have it also for MB

from the almighty AF

/* 0705: disable proxy direct failover for system requests [FF91+]
 * [WARNING] Default true is a security feature against malicious extensions [1]
 * [SETUP-CHROME] If you use a proxy and you trust your extensions
 * [1] https://blog.mozilla.org/security/2021/10/25/securing-the-proxy-api-for-firefox-add-ons/ ***/
   // user_pref("network.proxy.failover_direct", false);

cc: @pierov