user.js

// Don't show WhatsNew on first run after every update
user_pref("browser.startup.homepage_override.mstone","ignore");

//disable slowStartup Notification
user_pref("browser.slowStartup.notificationDisabled", true);
user_pref("browser.slowStartup.maxSamples", 0);
user_pref("browser.slowStartup.samples", 0);
user_pref("browser.rights.3.shown", true);
user_pref("startup.homepage_welcome_url", "");
user_pref("startup.homepage_welcome_url.additional", "");
user_pref("startup.homepage_override_url", "");
user_pref("browser.laterrun.enabled", false);
user_pref("browser.shell.checkDefaultBrowser", false);

//disable daily pings to Mozilla about extensions and recent startup
user_user("extensions.getAddons.cache.enabled", false);

//disable sending the URL of the website where a plugin crashed
user_pref("dom.ipc.plugins.reportCrashURL", false);

//disable auto update for extensions
user_user("extensions.update.autoUpdateDefault", false);

//disable about:addons' Get Add-ons panel (uses Google-Analytics)
user_pref("extensions.getAddons.showPane", false); // hidden user_pref
user_pref("extensions.webservice.discoverURL", "");

// Set default homepage - users can change
// Requires a complex preference
user_pref("browser.startup.homepage","data:text/plain,browser.startup.homepage=http://twiki.molgen.mpg.de/foswiki/Main/WebHome");

// Don't ask to install the Flash plugin
user_pref("plugins.notifyMissingFlash", false);

// Disable upload of health reports
user_pref("datareporting.healthreport.uploadEnabled", false);
//disable about:healthreport page (which connects to Mozilla for locale/css+js+json)
user_pref("datareporting.healthreport.about.reportUrl", "data:text/plain,");

// Disable all data upload (Telemetry and FHR)
user_pref("toolkit.telemetry.unified", false);
user_pref("toolkit.telemetry.enabled", false);
user_pref("toolkit.telemetry.server", "");
user_pref("toolkit.telemetry.newProfilePing.enabled", false);
user_pref("toolkit.telemetry.shutdownPingSender.enabled", false);
user_pref("toolkit.telemetry.updatePing.enabled", false);
user_pref("toolkit.telemetry.bhrPing.enabled", false);
user_pref("toolkit.telemetry.firstShutdownPing.enabled", false);
user_pref("toolkit.telemetry.cachedClientID", "");
user_pref("toolkit.telemetry.archive.enabled", false);
user_pref("datareporting.policy.dataSubmissionEnabled", false);
user_pref("browser.ping-centre.telemetry", false);

//disable "Snippets" (Mozilla content shown on about:home screen)
user_pref("browser.aboutHomeSnippets.updateUrl", "https://127.0.0.1"); //test

//disable experiments https://wiki.mozilla.org/Telemetry/Experiments
user_pref("experiments.enabled", false);
user_pref("experiments.manifest.uri", "");
user_pref("experiments.supported", false);
user_pref("experiments.activeExperiment", false);
// disable Mozilla permission to silently opt you into tests
user_pref("network.allow-experiments", false);

//disable pocket
user_pref("extensions.pocket.enabled", false);

//disable flyweb https://flyweb.github.io/
user_pref("dom.flyweb.enabled", false);

//disable Shield https://wiki.mozilla.org/Firefox/Shield
user_pref("extensions.shield-recipe-client.enabled", false);
user_pref("extensions.shield-recipe-client.api_url", "");

//disable Follow on Search and Activity Stream
user_pref("browser.newtabpage.activity-stream.enabled", false);
user_pref("browser.library.activity-stream.enabled", false);

//disable link-mouseover opening connection to linked server
user_pref("network.http.speculative-parallel-limit", 0);

//disable pings (but enforce same host in case)
user_pref("browser.send_pings", false);
user_pref("browser.send_pings.require_same_host", true);

//disable location bar using search - PRIVACY
user_pref("keyword.enabled", false);

//disable location bar domain guessing - PRIVACY/SECURITY
user_pref("browser.fixup.alternate.enabled", false);

//display all parts of the url in the location bar - helps SECURITY
user_pref("browser.urlbar.trimURLs", false);

//disable location bar making speculative connections (FF56+)
user_pref("browser.urlbar.speculativeConnect.enabled", false);

//disable SSL session tracking test
user_pref("security.ssl.disable_session_identifiers", true);

//disable SSL Error Reporting
user_pref("security.ssl.errorReporting.automatic", false);
user_pref("security.ssl.errorReporting.enabled", false);
user_pref("security.ssl.errorReporting.url", "");

//disable the DNT HTTP header, which is essentially USELESS
user_pref("privacy.donottrackheader.enabled", false);

//set max popups from a single non-click event - default is 20!
user_pref("dom.popup_maximum", 3);

//limit events that can cause a popup default is "change click dblclick mouseup pointerup notificationclick reset submit touchend"
user_pref("dom.popup_allowed_events", "click dblclick");

//enable Firefox's built-in PDF reader
user_pref("pdfjs.disabled", false);

//enable legacy extensions
user_pref("extensions.legacy.enabled",true);