If you want to add functionality to your web browser, you usually have the option to install extensions – or add-ons and plugins as some browsers call them – or userscripts.
Extensions are small programs that are loaded on the start of the web browser while userscripts only become active on the pages they have been designed for.
That is the biggest and most important difference between those two. Lets look at an example on how this sorts out. Lets say you are a big Facebook user and want to improve your experience on the social networking site by adding features and shortcuts to it.
Facebook Fixer is a userscript that might offer exactly what you are looking for. It can do all sorts of things like displaying bigger album pictures and photos, showing age information and signs, enabling keyboard shortcuts or automatic reloads on page errors.
A similar functionality is also provided by extensions like the Better Facebook Fixer extension for Google Chrome. It basically offers the same functionality as the userscript but with a small but noticeable difference.
I’m using Google Chrome for the example because it offers a task manager that lists the memory usage of all open tabs and extensions.
If you install the extension you notice that it uses about eight Megabytes of computer memory constantly. It runs in the background all the time even if you are not on Facebook or don’t have a single website open in Chrome.
The userscript on the other hand will only run when you visit Facebook.
It can generally be said that userscripts are more resource friendly than extensions. The situation is a little bit different for Firefox users who have to install an extension to use userscripts. But it is beneficial for them as well if we assume that the extensions will likely use a similar amount of computer memory meaning it is a tie if only one userscript is installed and an improvement if you install more than one.
This theory obviously only works if the extension and userscript offer a similar functionality.
There are a couple of other differences. Extensions may offer preferences or options that you can control from a manager that the browser ships with, while userscripts may require manual edits or provide you with options to change options when you visit one of the supported sites.
What do you prefer to use: Extensions or userscripts?