I should have replied sooner but I wanted to confirm the problem did not return after awhile but it has not. Thank you very much.
I installed Evernote and the Web Clipper. Now the Web Clipper appears frequently unbidden, meaning I have to click it closed so I can see the webpage. I thought it was not supposed to appear until I clicked on the icon to open it. I cannot find any setting to turn this off. Using iMac/OS 10.11.3/Safari, everything up to date.