Update: You can now use the built in feature under the settings menu in videos to change the playback speed. If you do not see playback speed controls, right click on the video and select 'switch to HTML5' then refresh the page.
To select a video playback speed, use the gear wheel in the lower right hand corner of the video as shown in this screenshot:
When you click the gear it expands to show playback speed options:
Let us know if you have any issues.