t: pref
i: /browser/branding/nightly/pref/firefox-branding.js
o: /browser/branding/nightly/pref/firefox-branding.js

+// Disable updates
+pref("app.update.enabled", false);
+pref("app.update.auto", false);
+pref("app.update.checkInstallTime", false);

+// Redirect update URLs to prevent fetching updates
+pref("app.update.url.manual", "https://localhost");
+pref("app.update.url.details", "https://localhost");
+pref("app.releaseNotesURL", "https://localhost");
+pref("app.releaseNotesURL.aboutDialog", "https://localhost");

+// Disable welcome and update pages
+pref("startup.homepage_override_url", "");
+pref("startup.homepage_welcome_url", "");
+pref("startup.homepage_welcome_url.additional", "");

+// Prevent update prompts
+pref("app.update.promptWaitTime", 0);
+pref("app.update.badgeWaitTime", 0);

+// Lock branding-related preferences (if applicable)
+pref("browser.startup.homepage", "about:blank");