How to intercept javascript?

Question

JavaScript

Hello, I started writing my extension for firefox, which would intercept all js code and put it in a file. the bottom line is that I googled and understood how to intercept a certain event, but there are a lot of buttons and different js on the site. I need to intercept only those scripts that are executed while I'm browsing the sites. there are also sites on which the scripts are not on the page itself, but with redirects, it is also possible that jqeury is connected. So how do I get the code that runs in the browser?