The toolbar popup can be used to change the video playback speed.
The "Control Speed Video" add-on makes it simple to change the playback speed for all HTML5 video components.
To use this plugin, open a HTML5 video-based website. Then, play the required video element and launch the toolbar popup UI. Set the playback speed in the UI, then click on Play (footer section). The playback speed will be adjusted dependent on the value displayed in the popup.
Please be aware that this add-on does not automatically change the speed. Each time you must open the toolbar popup UI and press the - Play - button (requires user action). Furthermore, every time a page is reloaded, the add-on requires another user action. The minimum and maximum speeds are 0.07x and 16x in accordance with HTML5 standards.