Firefox test suite issue

Hi everyone,

For some reason, Codepen says Firefox blocked the test suite(3rd party cookie) that is used for checking the responsive projects. I tried to clean the cache and individual cookies. I also checked the cookie setting, everything is fine.

I wonder if there is other things I can do instead of cleaning all my cookies?


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you have to add to the list of allowed third-party website cookies

I have tried it but it still shows message below.

“Test suites depend on access to localStorage. Please enable third-party cookies in the browser. See documentation for your browser for instructions on how to enable third-party cookies. Thanks and Happy Coding!”

I think the issue is with not Firefox, because if you use the test suite script in a local file it is going to work, you can try it.

This looks to be an issue specifically with Codepen, Firefox, and localStorage. The test uses localStorage and we have implemented a test for it to make sure the user is not blocking it. This is why you see the alert message.

I’m getting Uncaught DOMException: The operation is insecure when trying to set something to localStorage on Codepen in Firefox.

Here is a simple test that fails on Codepen in Firefox

It fails with modernizr as well.

Works fine on jsfiddle,, and codesandbox

Not really sure what is going on yet but one thing I did notice was the sandbox attribute for the iframe on Codepen does not have the allow-same-origin value which the other sites do have. Not sure if it’s the issue though.


sandbox="allow-downloads allow-forms allow-modals allow-pointer-lock allow-popups allow-presentation allow-scripts allow-top-navigation-by-user-activation"


sandbox="allow-modals allow-forms allow-scripts allow-same-origin allow-popups allow-top-navigation-by-user-activation allow-downloads"

sandbox="allow-forms allow-pointer-lock allow-popups allow-same-origin allow-scripts allow-modals"


sandbox="allow-forms allow-modals allow-popups allow-presentation allow-same-origin allow-scripts allow-downloads"

I don’t think there is much we can do about it on our end. It would seem to be an issue Codepen has to fix.

Edit: I send Codepen support a message about this.

Edit2: I got a response back from Codepen and they are looking into it.


Quick update:

This should be fixed now. I was right about the attribute value missing. Both the test script and video embeds should be back to working again. I tested it with the landing page project and everything works.

In case anyone is interested, here is the message I got back:

Hey there,

Yea. We finally figured out the issue. We accidentally removed an iFrame sandbox value allow-same-origin. It’s fixed and both examples work on FF again.

Thanks for taking the time to write in about the bug. This one was very frustrating.


Thank you @lasjorg for taking the time to work with codepen on resolving this issue.