So when I click on a new video, the thumbnail of the last video I watched appears in place of the video for 2 seconds and then the new video starts playing. Is there anything I can do to fix this? Maybe clear the cache or something?
Download the application YASU (Yet Another Mac Utility). I like it because it will delete caches, cookies and run daily, weekly and monthly built-in routines if you let it with a check mark!