JavaScript is a built-in programming language in browsers that allow website to create dynamic pages that aren't fixed. Some websites may not work with the Firefox 78 version you are using and that 78 version is the last version for your Mac OS X 10.10 operating system. In such a case you are out of luck. ---- Firefox 78.15.0 is the last version for your Mac OS X platform (update channel: mozilla-mac-eol-esr1) and you will no longer receive updates, so you are out of luck if you can't update your OS. Current releases require Mac OS X 10.12 or newer. *https://support.mozilla.org/en-US/kb/firefox-mac-osx-users-esr Firefox 78.15.0 on the Mozilla CDN server: *https://download-installer.cdn.mozilla.net/pub/firefox/releases/78.15.0esr/