This Firefox addon breaks a website

As clearly shown in the GIF below, this firefox addon breaks www.itjuzi.com
Only after both disabling the addon and cleaning the cookies, the website returns normal
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Strange issue, but I confirmed it. We will look into it.

Same issue in Chrome, but only with this specific website.

One workaround is to use desktop automation. So install the extension in a different browser and then open/automate the website in a second browser with desktop automation commands like XClick, XClickText etc.