Ok:
So...
Please disregard my prefs related to newtab and safebrowsing. I went through them one-by-one and this is what you need to add to your prefs.js or user.js (just make sure you remove the user.js afterwards)
user_pref("browser.newtab.preload", false);
user_pref("browser.newtabpage.activity-stream.asrouter.userprefs.cfr.addons", false);
user_pref("browser.newtabpage.activity-stream.asrouter.userprefs.cfr.features", false);
user_pref("browser.newtabpage.activity-stream.default.sites", "");
user_pref("browser.newtabpage.activity-stream.discoverystream.config", "");
user_pref("browser.newtabpage.activity-stream.discoverystream.endpoints", "");
user_pref("browser.newtabpage.activity-stream.feeds.aboutpreferences", false);
user_pref("browser.newtabpage.activity-stream.feeds.asrouterfeed", false);
user_pref("browser.newtabpage.activity-stream.feeds.discoverystreamfeed", false);
user_pref("browser.newtabpage.activity-stream.feeds.favicon", false);
user_pref("browser.newtabpage.activity-stream.feeds.newtabinit", false);
user_pref("browser.newtabpage.activity-stream.feeds.places", false);
user_pref("browser.newtabpage.activity-stream.feeds.prefs", false);
user_pref("browser.newtabpage.activity-stream.feeds.section.highlights", false);
user_pref("browser.newtabpage.activity-stream.feeds.section.topstories", false);
user_pref("browser.newtabpage.activity-stream.feeds.section.topstories.options", "");
user_pref("browser.newtabpage.activity-stream.feeds.sections", false);
user_pref("browser.newtabpage.activity-stream.feeds.snippets", false);
user_pref("browser.newtabpage.activity-stream.feeds.systemtick", false);
user_pref("browser.newtabpage.activity-stream.feeds.telemetry", false);
user_pref("browser.newtabpage.activity-stream.feeds.topsites", false);
user_pref("browser.newtabpage.activity-stream.filterAdult", false);
user_pref("browser.newtabpage.activity-stream.improvesearch.noDefaultSearchTile", false);
user_pref("browser.newtabpage.activity-stream.improvesearch.topSiteSearchShortcuts.searchEngines", "");
user_pref("browser.newtabpage.activity-stream.section.highlights.includeBookmarks", false);
user_pref("browser.newtabpage.activity-stream.section.highlights.includeDownloads", false);
user_pref("browser.newtabpage.activity-stream.section.highlights.includePocket", false);
user_pref("browser.newtabpage.activity-stream.section.highlights.includeVisited", false);
user_pref("browser.newtabpage.activity-stream.section.highlights.rows", 0);
user_pref("browser.newtabpage.activity-stream.section.topstories.rows", 0);
user_pref("browser.newtabpage.activity-stream.showSearch", false);
user_pref("browser.newtabpage.activity-stream.showSponsored", false);
user_pref("browser.newtabpage.activity-stream.telemetry.ping.endpoint", "");
user_pref("browser.newtabpage.activity-stream.telemetry.structuredIngestion.endpoint", "");
user_pref("browser.newtabpage.activity-stream.topSitesRows", 0);
user_pref("browser.newtabpage.enabled", false);
user_pref("browser.newtabpage.storageVersion", 1);
user_pref("browser.safebrowsing.blockedURIs.enabled", false);
user_pref("browser.safebrowsing.downloads.remote.block_dangerous", false);
user_pref("browser.safebrowsing.downloads.remote.block_dangerous_host", false);
user_pref("browser.safebrowsing.downloads.remote.block_potentially_unwanted", false);
user_pref("browser.safebrowsing.downloads.remote.block_uncommon", false);
user_pref("browser.safebrowsing.id", "");
user_pref("browser.safebrowsing.malware.enabled", false);
user_pref("browser.safebrowsing.phishing.enabled", false);
user_pref("browser.safebrowsing.prefixset_max_array_size", 0);
user_pref("browser.safebrowsing.provider.google.pver", "");
user_pref("browser.safebrowsing.provider.google4.pver", "");
user_pref("browser.safebrowsing.provider.mozilla.lists.base", "");
user_pref("browser.safebrowsing.provider.mozilla.lists.content", "");
user_pref("browser.safebrowsing.provider.mozilla.nextupdatetime", "");
user_pref("browser.safebrowsing.provider.mozilla.pver", "");