Labs and exams not available in Firefox (Silverlight issue)

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Firefox versions 52.0 and above no longer support Microsoft Silverlight. Silverlight is an NPAPI plugin which we use in some of our older courses and such plugins are gradually being supported by fewer and fewer browsers. IE 11 and Safari still support Silverlight but Firefox 52+, Chrome, and Edge do not. There is, however, a work-around offered by Mozilla that allows Silverlight support until early 2018. (See work-around below)

When clicking on a LabSim product that uses Silverlight, you will get the following message:

If you click "Launch without Labs or Exams" and then proceed to a lab and click "Start Lab", you would get the following error message:



Use Internet Explorer 11 or Safari to use these TestOut products or use the following workaround for Firefox.

Work-around:  (until early 2018)

Firefox explains their reasons for ending NPAPI plugin support and how to work around it here.

They provide the Firefox ESR 52 version* which will continue to support these plugins until early 2018.


(See video guide at the bottom of this page or follow the step by step guide below.)


Simply go to this URL, select the language and version you want based on your OS (If you have a 64-bit OS, both the 32 and 64-bit versions will work fine.)

Proceed to download and run the ESR version, finally opening the new version and continuing to enter TestOut/LabSim again.

*Custom exams and TestOut Certification exams will not function in any version of Firefox


When you click on the TestOut product that uses Silverlight again you will still get the below warning message but you should simply continue past it by clicking "Launch without Labs or Exams".


Proceed to the lab, click "Start Lab" and be sure to enable pop-ups from

Your lab should then proceed to load normally, assuming that Silverlight is properly installed on the machine.

For a video tutorial, see the attached .mp4 file or follow this link.