Quote:Firefox users who upgraded the web browser to version 63 released in October 2018 may notice that the browser does not accept JavaScript code anymore when entered in the address bar.

Previous versions of the web browser allowed users to write or paste JavaScript code in the address bar to execute it from there. You can try this out yourself by typing j‌avascript:alert("hello world") in the address bar and hitting Enter.

Previous versions of Firefox displayed the Hello World alert when executed but Firefox 63 blocks the execution and redirects the input to the default search engine instead. The same is true for any other JavaScript code that you enter in the address bar.

You may notice that j‌avascript: is removed when you paste code into the address bar but even if you add it manually, it won't be executed.

Full reading: https://www.ghacks.net/2018/10/24/firefox-63-blocks-javascript-in-address-bar-by-default/