@ageis's Firefox user settings (9/16/2019), hardened for security, privacy, and anti-fingerprinting, with some exceptions. Install into your profile, enter into about:config, replace channel-prefs or just use ghacks: https://github.com/ghacksuserjs/ghacks-user.js

channel-prefs.js

user_pref("accessibility.force_disabled", 1);
user_pref("alerts.showFavicons", false);
user_pref("app.normandy.api_url", "");
user_pref("app.normandy.enabled", false);
user_pref("app.shield.optoutstudies.enabled", false);

user_pref("app.update.auto", false);
user_pref("app.update.channel", "aurora");
user_pref("app.update.enabled", true);
user_pref("app.update.service.enabled", true);
user_pref("app.update.silent", true);
user_pref("app.update.staging.enabled", true);

user_pref("beacon.enabled", false);
user_pref("breakpad.reportURL", "");

user_pref("browser.cache.disk_cache_ssl", true);
user_pref("browser.cache.disk.capacity", 2457600);
user_pref("browser.cache.disk.enable", true);
user_pref("browser.cache.disk.smart_size.enabled", true);
user_pref("browser.cache.memory.enable", true);
user_pref("browser.cache.offline.enable", false);

user_pref("browser.chrome.errorReporter.enabled", false);
user_pref("browser.chrome.errorReporter.infoURL", "");
user_pref("browser.chrome.errorReporter.submitUrl", "");
user_pref("browser.crashReports.unsubmittedCheck.autoSubmit2", false);
user_pref("browser.crashReports.unsubmittedCheck.enabled", false);
user_pref("browser.discovery.enabled", false);
user_pref("browser.display.use_document_fonts", 0);
user_pref("browser.download.hide_plugins_without_extensions", false);
user_pref("browser.download.manager.addToRecentDocs", false);
user_pref("browser.download.useDownloadDir", false);
user_pref("browser.fixup.alternate.enabled", false);
user_pref("browser.fixup.hide_user_pass", true);
user_pref("browser.formfill.enable", false);
user_pref("browser.helperApps.deleteTempFileOnExit", true);
user_pref("browser.link.open_newwindow", 3);
user_pref("browser.link.open_newwindow.restriction", 0);

user_pref("browser.newtabpage.activity-stream.asrouter.providers.snippets", "");
user_pref("browser.newtabpage.activity-stream.disableSnippets", true);
user_pref("browser.newtabpage.activity-stream.feeds.discoverystreamfeed", false);
user_pref("browser.newtabpage.activity-stream.feeds.section.topstories", false);
user_pref("browser.newtabpage.activity-stream.feeds.snippets", false);
user_pref("browser.newtabpage.activity-stream.feeds.telemetry", false);
user_pref("browser.newtabpage.activity-stream.section.highlights.includePocket", false);
user_pref("browser.newtabpage.activity-stream.showSponsored", false);
user_pref("browser.newtabpage.activity-stream.telemetry", false);
user_pref("browser.newtabpage.activity-stream.telemetry.ping.endpoint", "");
user_pref("browser.newtabpage.enabled", false);
user_pref("browser.newtabpage.enhanced", false);

user_pref("browser.newtab.preload", false);
user_pref("browser.offline-apps.notify", true);
user_pref("browser.onboarding.enabled", false);
user_pref("browser.pagethumbnails.capturing_disabled", true);
user_pref("browser.ping-centre.telemetry", false);

user_pref("browser.safebrowsing.downloads.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.downloads.remote.enabled", false);
user_pref("browser.safebrowsing.malware.enabled", false);
user_pref("browser.safebrowsing.phishing.enabled", false);
user_pref("browser.safebrowsing.reportPhishURL", "");

user_pref("browser.search.countryCode", "US");
user_pref("browser.search.geoip.url", "");
user_pref("browser.search.geoSpecificDefaults", false);
user_pref("browser.search.geoSpecificDefaults.url", "");
user_pref("browser.search.region", "US");
user_pref("browser.search.reset.enabled", false);
user_pref("browser.search.reset.whitelist", "");
user_pref("browser.search.suggest.enabled", false);
user_pref("browser.search.update", false);

user_pref("browser.send_pings", false);
user_pref("browser.send_pings.require_same_host", true);
user_pref("browser.sessionhistory.max_entries", 10);
user_pref("browser.sessionstore.interval", 30000);
user_pref("browser.sessionstore.privacy_level", 2);
user_pref("browser.sessionstore.resume_from_crash", false);
user_pref("browser.shell.checkDefaultBrowser", false);
user_pref("browser.shell.shortcutFavicons", false);
user_pref("browser.ssl_override_behavior", 1);
user_pref("browser.startup.blankWindow", false);
user_pref("browser.startup.homepage", "about:blank");
user_pref("browser.startup.page", 0);
user_pref("browser.tabs.crashReporting.sendReport", false);
user_pref("browser.tabs.remote.allowLinkedWebInFileUriProcess", false);
user_pref("browser.tabs.remote.separateFileUriProcess", true);
user_pref("browser.tabs.warnOnClose", false);
user_pref("browser.tabs.warnOnCloseOtherTabs", false);
user_pref("browser.tabs.warnOnOpen", false);
user_pref("browser.taskbar.lists.enabled", false);
user_pref("browser.taskbar.lists.frequent.enabled", false);
user_pref("browser.taskbar.lists.recent.enabled", false);
user_pref("browser.taskbar.lists.tasks.enabled", false);
user_pref("browser.taskbar.previews.enable", false);
user_pref("browser.uitour.enabled", false);
user_pref("browser.uitour.url", "");

user_pref("browser.urlbar.autocomplete.enabled", false);
user_pref("browser.urlbar.autoFill", false);
user_pref("browser.urlbar.autoFill.typed", false);
user_pref("browser.urlbar.filter.javascript", true);
user_pref("browser.urlbar.oneOffSearches", false);
user_pref("browser.urlbar.speculativeConnect.enabled", false);
user_pref("browser.urlbar.suggest.history", false);
user_pref("browser.urlbar.suggest.searches", false);
user_pref("browser.urlbar.trimURLs", false);
user_pref("browser.urlbar.usepreloadedtopurls.enabled", false);
user_pref("browser.urlbar.userMadeSearchSuggestionsChoice", true);

user_pref("browser.xul.error_pages.expert_bad_cert", true);
user_pref("browser.zoom.siteSpecific", false);
user_pref("captivedetect.canonicalURL", "");
user_pref("clipboard.autocopy", false);
user_pref("datareporting.healthreport.infoURL", "");
user_pref("datareporting.healthreport.service.enabled", false);
user_pref("datareporting.healthreport.uploadEnabled", false);
user_pref("datareporting.policy.dataSubmissionEnabled", false);
user_pref("device.sensors.ambientLight.enabled", false);
user_pref("device.sensors.enabled", false);
user_pref("device.sensors.motion.enabled", false);
user_pref("device.sensors.orientation.enabled", false);
user_pref("device.sensors.proximity.enabled", false);
user_pref("device.storage.enabled", true);
user_pref("devtools.chrome.enabled", false);
user_pref("devtools.debugger.remote-enabled", false);
user_pref("devtools.webide.adbAddonURL", "");
user_pref("devtools.webide.autoinstallADBExtension", false);
user_pref("devtools.webide.autoinstallADBHelper", false);
user_pref("devtools.webide.enabled", false);
user_pref("dom.allow_cut_copy", false);
user_pref("dom.allow_scripts_to_close_windows", false);
user_pref("dom.battery.enabled", false);
user_pref("dom.disable_beforeunload", true);
user_pref("dom.disable_open_during_load", true);

user_pref("dom.disable_window_move_resize", true);
user_pref("dom.disable_window_open_feature.close", true);
user_pref("dom.disable_window_open_feature.location", true);
user_pref("dom.disable_window_open_feature.menubar", true);
user_pref("dom.disable_window_open_feature.minimizable", true);
user_pref("dom.disable_window_open_feature.personalbar", true);
user_pref("dom.disable_window_open_feature.resizable", true);
user_pref("dom.disable_window_open_feature.status", true);
user_pref("dom.disable_window_open_feature.titlebar", true);
user_pref("dom.disable_window_open_feature.toolbar", true);

user_pref("dom.enable_performance", false);
user_pref("dom.enable_resource_timing", false);
user_pref("dom.enable_user_timing", false);
user_pref("dom.event.clipboardevents.enabled", false);
user_pref("dom.event.highrestimestamp.enabled", true);
user_pref("dom.flyweb.enabled", false);
user_pref("dom.indexedDB.enabled", true);
user_pref("dom.ipc.plugins.flash.subprocess.crashreporter.enabled", false);
user_pref("dom.ipc.plugins.reportCrashURL", false);
user_pref("dom.netinfo.enabled", false);
user_pref("dom.network.enabled", false);
user_pref("dom.popup_allowed_events", "click dblclick");
user_pref("dom.serviceWorkers.enabled", false);
user_pref("dom.storage_access.enabled", true);
user_pref("dom.storage.enabled", true);
user_pref("dom.targetBlankNoOpener.enabled", true);
user_pref("dom.telephony.enabled", false);
user_pref("dom.vibrator.enabled", false);
user_pref("dom.vr.enabled", false);
user_pref("dom.w3c_pointer_events.enabled", false);
user_pref("dom.webaudio.enabled", true);
user_pref("experiments.activeExperiment", false);
user_pref("experiments.enabled", false);
user_pref("experiments.manifest.uri", "");
user_pref("experiments.supported", false);

user_pref("extensions.autoDisableScopes", 15);
user_pref("extensions.blocklist.enabled", true);
user_pref("extensions.blocklist.url", "https://blocklists.settings.services.mozilla.com/v1/blocklist/3/%APP_ID%/%APP_VERSION%/");
user_pref("extensions.enabledScopes", 5);
user_pref("extensions.formautofill.addresses.enabled", false);
user_pref("extensions.formautofill.available", "off");
user_pref("extensions.formautofill.creditCards.enabled", false);
user_pref("extensions.formautofill.heuristics.enabled", false);
user_pref("extensions.getAddons.showPane", false);
user_pref("extensions.htmlaboutaddons.recommendations.enabled", false);
user_pref("extensions.pocket.enabled", false);
user_pref("extensions.systemAddon.update.enabled", false);
user_pref("extensions.systemAddon.update.url", "");
user_pref("extensions.update.autoUpdateDefault", true);
user_pref("extensions.update.enabled", true);
user_pref("extensions.webcompat-reporter.enabled", false);

user_pref("geo.enabled", false);
user_pref("geo.provider.ms-windows-location", false);
user_pref("geo.provider.use_corelocation", false);
user_pref("geo.provider.use_gpsd", false);
user_pref("geo.wifi.uri", "https://location.services.mozilla.com/v1/geolocate?key=%MOZILLA_API_KEY%");
user_pref("gfx.font_rendering.graphite.enabled", false);
user_pref("gfx.font_rendering.opentype_svg.enabled", false);
user_pref("intl.accept_languages", "en-US, en");
user_pref("intl.locale.requested", "en-US");
user_pref("intl.regional_prefs.use_os_locales", false);
user_pref("javascript.options.asmjs", false);
user_pref("javascript.options.wasm", true);
user_pref("javascript.use_us_english_locale", true);
user_pref("keyword.enabled", false);
user_pref("layout.css.visited_links_enabled", false);
user_pref("lightweightThemes.update.enabled", false);
user_pref("media.autoplay.enabled", false);
user_pref("media.autoplay.enabled.user-gestures-needed", false);
user_pref("media.autoplay.enabled.user-gestures-needed", true);
user_pref("media.block-autoplay-until-in-foreground", true);
user_pref("media.eme.enabled", false);
user_pref("media.getusermedia.audiocapture.enabled", false);
user_pref("media.getusermedia.browser.enabled", false);
user_pref("media.getusermedia.screensharing.enabled", false);
user_pref("media.gmp-gmpopenh264.enabled", false);
user_pref("media.gmp-widevinecdm.enabled", false);
user_pref("media.gmp-widevinecdm.visible", false);
user_pref("media.navigator.enabled", false);
user_pref("media.ondevicechange.enabled", false);
user_pref("media.peerconnection.enabled", false);
user_pref("media.peerconnection.ice.default_address_only", true);
user_pref("media.peerconnection.ice.no_host", true);
user_pref("media.video_stats.enabled", false);
user_pref("media.webspeech.synth.enabled", false);
user_pref("middlemouse.contentLoadURL", false);
user_pref("middlemouse.paste", false);

user_pref("network.allow-experiments", false);
user_pref("network.auth.subresource-http-auth-allow", 1);
user_pref("network.captive-portal-service.enabled", false);
user_pref("network.connectivity-service.enabled", false);
user_pref("network.cookie.cookieBehavior", 1);
user_pref("network.cookie.thirdparty.nonsecureSessionOnly", true);
user_pref("network.cookie.thirdparty.sessionOnly", true);
user_pref("network.dns.disableIPv6", true);
user_pref("network.dns.disablePrefetchFromHTTPS", true);
user_pref("network.dns.disablePrefetch", true);
user_pref("network.file.disable_unc_paths", true);
user_pref("network.gio.supported-protocols", "");
user_pref("network.http.altsvc.enabled", false);
user_pref("network.http.altsvc.oe", false);
user_pref("network.http.redirection-limit", 10);
user_pref("network.http.referer.hideOnionSource", true);
user_pref("network.http.referer.spoofSource", true);
user_pref("network.http.referer.XOriginPolicy", 1);
user_pref("network.http.referer.XOriginTrimmingPolicy", 0);
user_pref("network.http.sendOriginHeader", 0);
user_pref("network.http.sendRefererHeader", 0);
user_pref("network.http.speculative-parallel-limit", 0);
user_pref("network.IDN_show_punycode", true);
user_pref("network.jar.block-remote-files", true);
user_pref("network.jar.open-unsafe-types", false);
user_pref("network.manage-offline-status", false);
user_pref("network.predictor.enabled", false);
user_pref("network.predictor.enable-prefetch", false);
user_pref("network.prefetch-next", false);
user_pref("network.protocol-handler.external.ms-windows-store", false);
user_pref("network.proxy.socks_remote_dns", true);
user_pref("network.stricttransportsecurity.preloadlist", true);
user_pref("network.trr.mode", 3);
user_pref("network.trr.uri", "https://cloudflare-dns.com/dns-query");

user_pref("offline-apps.allow_by_default", false);
user_pref("pdfjs.disabled", false);
user_pref("permissions.manager.defaultsUrl", "");
user_pref("plugins.click_to_play", true);
user_pref("plugin.state.flash", 0);
user_pref("plugin.state.java", 0);

user_pref("privacy.clearOnShutdown.cache", true);
user_pref("privacy.clearOnShutdown.cookies", false);
user_pref("privacy.clearOnShutdown.downloads", true);
user_pref("privacy.clearOnShutdown.formdata", true);
user_pref("privacy.clearOnShutdown.history", true);
user_pref("privacy.clearOnShutdown.offlineApps", true);
user_pref("privacy.clearOnShutdown.sessions", false);
user_pref("privacy.clearOnShutdown.siteSettings", false);

user_pref("privacy.cpd.cache", true);
user_pref("privacy.cpd.cookies", false);
user_pref("privacy.cpd.downloads", true);
user_pref("privacy.cpd.formdata", true);
user_pref("privacy.cpd.history", true);
user_pref("privacy.cpd.offlineApps", true);
user_pref("privacy.cpd.passwords", false);
user_pref("privacy.cpd.sessions", false);
user_pref("privacy.cpd.siteSettings", false);

user_pref("privacy.donottrackheader.enabled", true);
user_pref("privacy.firstparty.isolate.restrict_opener_access", true);
user_pref("privacy.firstparty.isolate", true);
user_pref("privacy.resistFingerprinting.block_mozAddonManager", true);
user_pref("privacy.resistFingerprinting.letterboxing", true);
user_pref("privacy.resistFingerprinting", true);
user_pref("privacy.sanitize.sanitizeOnShutdown", true);
user_pref("privacy.sanitize.timeSpan", 0);
user_pref("privacy.trackingprotection.enabled", true);
user_pref("privacy.trackingprotection.socialtracking.enabled", true);
user_pref("privacy.usercontext.about_newtab_segregation.enabled", true);
user_pref("privacy.userContext.enabled", true);
user_pref("privacy.userContext.longPressBehavior", 2);
user_pref("privacy.userContext.ui.enabled", true);

user_pref("reader.parse-on-load.enabled", false);

user_pref("security.ask_for_password", 1);
user_pref("security.certerrors.recordEventTelemetry", false);
user_pref("security.cert_pinning.enforcement_level", 2);
user_pref("security.csp.enable", true);
user_pref("security.csp.enable_violation_events", false);
user_pref("security.csp.experimentalEnabled", true);
user_pref("security.dialog_enable_delay", 700);
user_pref("security.family_safety.mode", 0);
user_pref("security.fileuri.strict_origin_policy", true);
user_pref("security.insecure_connection_icon.enabled", true);
user_pref("security.insecure_connection_text.enabled", true);
user_pref("security.insecure_password.ui.enabled", true);
user_pref("security.mixed_content.block_active_content", true);
user_pref("security.mixed_content.block_display_content", true);
user_pref("security.mixed_content.block_object_subrequest", true);
user_pref("security.mixed_content.upgrade_display_content", true);
user_pref("security.OCSP.enabled", 1);
user_pref("security.OCSP.require", true);
user_pref("security.password_lifetime", 60);
user_pref("security.pki.sha1_enforcement_level", 1);
user_pref("security.sri.enable", true);

user_pref("security.ssl.disable_session_identifiers", true);
user_pref("security.ssl.enable_ocsp_stapling", true);
user_pref("security.ssl.errorReporting.automatic", false);
user_pref("security.ssl.errorReporting.enabled", false);
user_pref("security.ssl.errorReporting.url", "");
user_pref("security.ssl.require_safe_negotiation", true);
user_pref("security.ssl.treat_unsafe_negotiation_as_broken", true);
user_pref("security.tls.enable_0rtt_data", false);
user_pref("security.tls.version.max", 4);
user_pref("security.tls.version.min", 3);

user_pref("services.sync.enabled", true);
user_pref("shield.savant.enabled", false);
user_pref("signon.autofillForms", false);
user_pref("signon.formlessCapture.enabled", false);
user_pref("signon.storeWhenAutocompleteOff", true);
user_pref("toolkit.coverage.endpoint.base", "");
user_pref("toolkit.coverage.opt-out", true);

user_pref("toolkit.telemetry.archive.enabled", false);
user_pref("toolkit.telemetry.bhrPing.enabled", false);
user_pref("toolkit.telemetry.cachedClientID", "");
user_pref("toolkit.telemetry.coverage.opt-out", true);
user_pref("toolkit.telemetry.ecosystemtelemetry.enabled", false);
user_pref("toolkit.telemetry.enabled", false);
user_pref("toolkit.telemetry.firstShutdownPing.enabled", false);
user_pref("toolkit.telemetry.hybridContent.enabled", false);
user_pref("toolkit.telemetry.newProfilePing.enabled", false);
user_pref("toolkit.telemetry.reportingpolicy.firstRun", false);
user_pref("toolkit.telemetry.server", "");
user_pref("toolkit.telemetry.shutdownPingSender.enabled", false);
user_pref("toolkit.telemetry.unified", false);
user_pref("toolkit.telemetry.updatePing.enabled", false);

user_pref("toolkit.winRegisterApplicationRestart", false);
user_pref("ui.use_standins_for_native_colors", true);
user_pref("view_source.editor.external", true);
user_pref("view_source.editor.path", "/usr/bin/code");
user_pref("view_source.tab", false);
user_pref("view_source.wrap_long_lines", true);
user_pref("webchannel.allowObject.urlWhitelist", "");

user_pref("webgl.disabled", true);
user_pref("webgl.disable-extensions", true);
user_pref("webgl.disable-fail-if-major-performance-caveat", true);
user_pref("webgl.dxgl.enabled", false);
user_pref("webgl.enable-debug-renderer-info", false);
user_pref("webgl.enable-webgl2", false);
user_pref("webgl.min_capability_mode", true);