Make sure safebrowsing is still disabled in ESR 52

Safebrowsing prefs got renamed and features got added. We should make sure Safebrowsing is still disablled in ESR 52, though. For starters we could set

browser.safebrowsing.downloads.enabled = false browser.safebrowsing.downloads.remote.enabled = false browser.safebrowsing.malware.enabled = false browser.safebrowsing.phishing.enabled = false browser.safebrowsing.blockedURIs.enabled = false