I'm tired of browsing settings to change the playback speed of YouTube videos, so I made this bookmarklet to add controls to the bottom bar (speed up and slow down buttons and a label to see current playback speed).
You can add the bookmarklet creating a new bookmark with any name (e.g. YTSpeed) and this code in the URL field.
Press the bookmark to add controls, press again to hide them.
Use "+" button to increase speed of 0.1x and "-" button to decrease speed of 0.1x.