Some time ago, Youtube introduced it's 'just in time (JIT) buffering' in an effort to curtail excessive network traffic to their service. Previous to this change, a paused video would continue to download the video and store it on your machine (buffering) to be ready to play, but JIT buffering changed this to only buffer the next few seconds of video (this saves their resources when someone has buffered a video but only watches the first portion of it). While this change helped alleviate the load on their own servers, it removed the buffer that would allow a streaming video to continue playing without the interruption to pause and catch up to itself.
Magic Actions is an add-on for Firefox or Chrome that allows you to turn this buffering back on.
To install Magic actions, head to their site here: Magic Actions for Youtube, and click the Add to Chrome or Add to Firefox options and follow the prompts. Once you have added it, you will have to restart your Firefox or Chome for it to be active. The new icons that show under a youtube video will indicate that it is active:
After it's active, hit that gear icon to into the settings to make the adjustments to fix the buffering, as well as disabling the annoying autoplay, and setting the default playback to 480p for smoothness. You'll have to restart your Firefox or Chome to apply the settings after making any adjustments. Here's an image of the settings you'll want to use:
The 480p playback setting is a happy medium for quality and smooth playback, it's a great default. You can still use the youtube controls to change it up or down on individual videos with this active.
'Stop Autoplay' stops the videos from playing automatically, just give them a click to get them playing. 'Don't stop in a playlist' should be checked along with this to prevent having to start every video when watching a playlist.
The speed booster fixes the buffering so that the video is less likely to catch up to itself and get stuck.
Keywords: youtube, magic actions, stop autoplay, set playback, fix buffering