k1326195
Implied in @diana_benavides 's post is that your browser is most likely not up to date. There seem to be several people having problems with Safari and Canvas recently and the answer that is going around is to update the browser to a recent version. I know that when one of my students complained about the issue, he hadn't updated his operating system in a while.
Since Safari is part of the Mac OS, you will need to update the operating system to update Safari. Here are a couple of links about how to do this from the Apple support site:
Switching to Chrome may not work. The latest (and supported) versions of Chrome are not available for older Mac operating systems, either.
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