If I try https://www.proctoru.com/firefox I see the same thing. There was a similar thread two weeks ago (has a screenshot, but no solution): https://support.mozilla.org/questions/1389072

I think this means that the extension was reported to Mozilla to cause problems so it is temporarily blocked until it is fixed. You might need to use Google Chrome for this test, assuming their Chrome extension is still working.

In case the company isn't aware of the problem, you may want to report it to them for the benefit of all Firefox users. https://www.meazurelearning.com/contact-us

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