Just recently I've noticed something - There are a few web sites that if I leave Safari on those sites for very long, the amount of memory that they use keeps going up and eventually reaches fantastic levels. The worst offenders by far are Weather.Com and FoxNews.Com. I left Safari on weather.com earlier this morning and about 15 minutes later came back to an extremely sluggish computer. I started up Activity Monitor and discovered that there was 24 GB of memory being used by weather.com. My computer only has 12 GB of memory! So it must have been swapping almost continuously with the hard drive. I tried some other web sites and most behaved, but FoxNews started out at about 250 MB and creeping up, and after 20 minutes was using 9 GB. Googled for awhile and found that apparently Safari is famous for "memory leak" for many years - but at least on my system this is something new. Maybe since the last software update?. OS X 10.11.6? There are some "fixes" out there in the internet but none of them seem to work for me. Doesn't seem to be a problem as long as I spend less than a few minutes at a time on weather.com or foxnews.com.