So, the number of extensions is growing rapidly. But how can one benefit from an extension? Well, if you are a user-js geek, first, think of Opera extensions as of always up-to-date 3d party user-js scripts. The provided browser communication API for managing windows, tabs, toolbars, icons etc. makes a complete picture. Yet, a user-js is just a script that can be initially triggered at various page loading stages. Every extension, for starters, has it's own process constantly running in background... But why discuss technical issues? I'm sure a geek can find a way to create an extension in 30 minutes. (Hopefully all geeks have followed that link :)
I believe, there is no need to explain, what YouTube is. The widely-used video hosting service already got it's fair share of Opera extensions. Would you like to find out what features these wonderful extensions are capable of?
Easy Youtube Downloader for Opera [⇩]
The extension provides an easy and convenient way to download YouTube videos in all available formats, including mp3 (through the videodroid.org service).
The extension creates a Download As: drop-down list with one or more direct links to video files. If you're not familiar with "p" notation, "p" stands for horizontal scan lines of display resolution (also known as number of vertical resolution pixels) . The very basic idea here is: the bigger - the better.
In case you don't know what should be chosen from 360p options  , a simple answer would be: "360p FLV has better resolution". Consequently, the file size will differ a bit too. For example, the Opera Unite intro video's size is 4.4 MB (MP4) versus 5.2 MB (FLV).
Bored of watching low-res movies? Hit highest available HD option (720p or 1080p) and download the clip in High Definition.
Easy Youtube Downloader is not the one of it's kind, yet is the best available. Even with minor advantages (an icon on download button and "MP3" download option) it beats the Fastest Youtube Video Downloader and Youtube Downloader 2 extensions.
Focus on Videos [⇩]
Focus on Videos is a nice extension that deems everything but the video you're watching. As a video starts playing, the extension turns this
You can also toggle that by clicking a control button with a green lamp icon on it, or hitting Escape button (yeah, the one that's in the right top corner of the keyboard :).
This focus effect is especially perfect if browser is running in Full screen mode.
YouTube AdsFree [⇩]
An extension that makes user's dream come true. As a user, I'm very embarrassed with these kind of ads:
Fortunately, YouTube AdsFree extension solves the problem once and for all. Eventually Google will have to invent another way of showing YouTube ads to Opera users.
You have to re-open the page with a video to make extension work. (In this case, Ctrl+W; Ctrl+Z will save you a couple of mouse clicks!)
A minor, yet often required feature that a standard player lacks: video playback loop. LoopTube is a small extension that makes our live easier by providing that feature. You can manage it's behaviour via additional control button:
Youtube Autoplay Killer [⇩] Another heavily demanded feature. Not only the extension disables auto-play, it also holds the download process (very useful, e.g. if you just want to read the comments, yet very annoying, if you have a slow connection and want to cache the video before watching it).
A small drawback: the extension doesn't work with HTML5 videos (which are discussed below), but that's version 1.0 we're talking about!
Searching for videos
YouTube WebM Enablr [⇩] Do you know that the <video> tag was proposed by Opera back in 2007? That was almost 4 years ago! Nowadays we're slowly moving from Adobe Flash-embedded videos to HTML5 video system.
WebM is a multimedia container format designed to provide a royalty-free, high-quality open video compression format for use with HTML5 video .
In my opinion, the key words here are: royalty-free, high-quality, open. There were loud debates (I wonder if they are finished) about the format . Still, what concerns Opera users is that WebM is fully supported by Opera, and if you have a trouble running Adobe Flash plug-in, then WebM Enablr is just what the doctor ordered.
The steps are simple: 1. Install the extension. 2. Search for videos. 3. Watch video without Flash plugin involved.
WebM videos only! There are plenty of YouTube clips that haven't been encoded in WebM yet. And don't rely on playlist-based search results. Those still might require Adobe Flash plugin.
So many of them...
Of course, this is not the complete list of YouTube-specific extensions. Hopefully this small suite will suit your basic needs. Don't hesitate a moment to try them all !