Installing a JavaScript file

Solution 1:

Thoroughly read the Installing Greasemonkey Scripts guide. Firefox is the browser that is recommended by userscripts.org for using their scripts. Userscripts in Firefox run via the Greasemonkey Firefox add-on. Greasemonkey allows you to customize the way a web page displays or behaves, by using small bits of JavaScript.

From the Installing Greasemonkey Scripts guide:

Now that you have Firefox, you need to install Greasemonkey. After installation (which requires restarting your browser), you are now ready to install userscripts.

Now clicking on a .user.js link triggers Greasemonkey to pop up the script installation panel. Greasemonkey shows you a list of what sites the script will run on and ask if you want to install the script.

Now loading a web page results in additional code (the userscript) being run.