Add userscript feature

I want to be able to install userScript. Because I can customize the website myself.

Could you explain in detail what you want to achieve?
Javascript is not something you install. Javascript is a coding language that is interpreted by the browser itself.

Which website do you wan to customise? Websites are hosted in a server. So, you need to have access to it. And this has nothing to do with the browser.

If you mean, you want to change the way you see things when you load a website, you can do it using developer tools (press F12). However you are not changing the website, but just your view. Next time you load the same website those changes are gone.

Check this extension

Sorry for my poor explanation.
What I want to do is to use a script from a site called Greasy Fork, I wrote that Safari has scripts available, but Brave did not, so I want scripts to be available.

But you still did not explain what you are trying to achieve.

Javascript scripts are embedded in a webpage source code, in its server. This is nothing you do in your browser.

When you load a webpage, it loads the source code which is interpreted and processed by your browser.

From the browser side you cannot change the original source code or a webpage behaviour.

The alternatives I gave you allows you to change the view in your browser, but it will not change the webpage behaviour, as you cannot change anything that runs in the server side.

Perhaps, if you could explain us what you want to achieve, it would be easier to guide you.

I think he want a feature like chrome extension called “tampermonkey”. It can run JS script on client side

I agree, I saw the replies to the questions and just had to laugh at the level of misunderstanding.