This seems odd. My first thought was to wonder if there is a specific extension causing the issue. Are any of them related to Canvas? Second would be to ask if quizzes was working correctly before adding the extensions? That would definitely imply the extensions are the cause if it did work.
Without knowing specifically which extensions were added (and if it worked before adding them), it would be hard to determine what might be causing this issue for you. If you have another computer without the extensions, you could try that too.
As for testing it, have you tried the Preview option to see if that shows it working for you?