Wikipedia is a useful resource for all kinds of things, but it's ugly and not all that customisable. With just a few extensions and tricks, you can make it a lot more usable.
Use Simple English Wikipedia to Better Understand Complex Subjects
Wikipedia is already simplified, but a lot of its articles are still really difficult to understand. Simple English Wikipedia can help you understand complex subjects.
The basic idea with Simple English Wikipedia is that it skips the complex terms so anyone can understand a complicated subject. For example, this article on black holes ditches the complex physics terms and wordiness of the original Wikipedia article so it's easy to understand.
Use Wikipedia's Date View to Keep Up with Current Events
It's hard to catch up on the news after taking a holiday or ignoring current events for a little while, but Wikipedia's date view makes it easy to see important events at a glance. Just type in the day or month you missed out on, and Wikipedia will show you all the big news stories in a simple list.
Unlock Wikipedia's Beta Features
Last year, Wikipedia announced that it would let users check out beta features. Right now, these include a media viewer, a new editor, a new visual editor, new typography, a new search box and hovercards. All you need to do to test these out is to log into your Wikipedia account (or create one), then head to the beta features section to enable the features you want to test. Some, like the hovercards, which adds a popup to links and new functionality to the site.
Create Ebooks with a Click
Sometimes, you don't have access to the internet and for those moments it's useful to create ebook versions of Wikipedia pages. All you have to do is click the "Print/Export" button on the left side of a Wikipedia page, and then select "Create a book". From here, you can create your own custom books based on any pages you want then export it as a PDF or EPUB.
Add YouTube Videos to Articles
Wikipedia is great for learning about all kinds of topics, but sometimes you need to watch a video for something to really sink in. WikiTube is a Chrome extension that adds relevant YouTube videos to the top of Wikipedia pages so you can easily get context for the pages you're reading. Firefox users can use Wikipedia Advanced to get a similar function with the extension's YouTube integration.
Search Wikipedia from Anywhere
You don't always want to go all the way to Wikipedia just to read a little bit about a topic. Sometimes, all you need is a quick, dictionary-like button to instantly glance at the page for a particular work. For that, we like Lookup Companion for Chrome and QuickWiki for Firefox. Lookup Companion adds a small popup to your toolbar where you can quickly search for a word. QuickWiki allows you to right-click any word on a page to search for it on Wikipedia.
Follow Wikipedia Links without Leaving the Page
For when you just need to glance at a definition, it's nice to mouse over a word on Wikipedia and get a brief description of that page. Wikipedia Quick Hints for Chrome is a simple way to add this functionality. Once it's installed, just drag your mouse over a link, and you'll see a short preview of that article. Firefox users can use Wikipedia Advanced to get a similar description, although you'll also have all the other features of the extension.
Skin Wikipedia with One of These Extensions
Wikipedia is one of the uglier sites on the internet and it's often difficult to read longer articles. If you want to clean up the interface a bit, you have a few different options.
Better Wikipedia (Chrome/Firefox) is an all-encompassing extension that overhauls the look of Wikipedia from the ground up. It includes a cleaner reading experience, a navigation bar, related videos, a new summary section for timelines, link previews, and more.
Readable Wikipedia for Chrome takes a different approach and cuts out all the clutter on Wikipedia so it's easier to read. It looks a lot like the result you'd get from pushing an article through Readability (which is another option and good for Firefox users).
Finally, if you want a bit more control over Wikipedia's look, a lot of various Stylish (Chrome/Firefox) styles exist that overall the look in all kinds of ways. Of course, you can always use Wikipedia's own skins too.