JavaScript is a scripting language that adds interactivity to plain HTML web pages. Firefox gives you the ability to disable it.

Just go to the top of your browser and click Tools > Options:

 

 

The “Options” window will open.

Make sure you are in the “Content” section.

I highlighted below where you can find the checkbox to enable/disable JavaScript:

 

 

If you’d like to keep JavaScript enabled, you can still disable certain actions that a script may try to perfom.

Click on the “Advanced” button.

 

 

The “Advanced JavaScript Settings” will open:

 

 

As you can see, even though you have JavaScript enabled, you can refuse to allow a script to “Move or resize existing windows,” or “Hide the status bar,” etc.