Hi

Are you trying to learn how to code, or is there a specific website that isn't loading correctly for you?

You don't need to add JavaScript to Firefox. It is built-in and enabled by default.

If websites are telling you "JavaScript is disabled," someone might have turned it off in. check:

Type about:config

Search javascript.enabled

If it says false, double-click it (or click the toggle button on the right) to set it to true.

Is this with the Firefox for Android you are posting with or with desktop Firefox on Windows, macOS, Linux.

With desktop Firefox just type about:config in the location (address) bar like you would type in example.com

https://support.mozilla.org/en-US/kb/about-config-editor-firefox

With the Firefox for Android, only the Beta and Nightly development channel builds have about:config and not the Release channel.