JavaScript is enabled by default in Firefox, you can check or change the setting through the browser's advanced configuration page. Open Firefox and type about:config into the address bar. search javascript.enabled. The search results will show the javascript.enabled preference. Its value should be set to true. If it's false, double-click the row to change the value back to true. Restart your browser. [https://support.mozilla.org/en-US/kb/javascript-settings-for-interactive-web-pages| JavaScript settings and preferences for interactive web pages]