Controls for YouTube
is a Google Chrome extension which adds... controls for YouTube. Specifically, it adds fast-forward and rewind buttons over by the other controls. I made this userstyle so that those buttons more closely match the original YouTube interface. You MUST have that extension installed in order for this to do anything. I am not the author of that extension, so I cannot help you if you're having issues with it.
Install the extension from here:https://chrome.google.com/webstore/detail/controls-for-youtube/doocmbmlcnbbdohogchldhlikjpndpngMake sure that the buttons are enabled in the extension's config screen.
I forget if they're on or off by default.