Totem Filling Up Cache

Today, I got a warning about low disk space in my /home folder, which I thought was odd, considering that I keep all my data on a separate Data partition. Using the disk usage analyzer, I discovered that my /.cache folder was a whopping 27 GB! Opening it up, I discovered that since April, totem-plugin-viewer has been saving a complete copy of every video I've watched on YouTube and Facebook (every video is titled totem-plugin-viewer-XXXXXX). There's over 500 of them stored there. Needless to say, I've deleted them all, and solved the low disk space problem.

I use GreaseMonkey with ViewTube to watch the videos online, and did a test. Sure enough, when I loaded up a video on YouTube, a new file was created in /.cache, where it was copying the video. How can I get it to stop doing this?