HD filling up with cached data?
I had the same problem; wrote the following bash script and run it once daily with cron. Problem solved. When I first noticed this, I had over 50GB in the fsCacheData folder!

#!/bin/bash
DIR=/private/var/folders/6m/36p_j3ss0zjbfjh3r72qjtw40000gn/C/com.apple.WebKit.Plugin.64/fsCachedData/
LIMIT=1                 
SIZE=$(du -h $DIR | cut -f 1)           

if [[ "${SIZE%?}" -ge $LIMIT ]];
    rm -r $DIR
fi