Solution: The error may occur because of browser extensions/addons. Could please the agent send us the screenshot of addons installed in their browser so we can investigate further ? In Mozzila Firefox it can be found in Menu => Add-ons and themes.
The issue occurs on every page the user opens and we're trying to resolve it. The error occurs because of installed extensions in user's browser. These browser extensions - such us anti-virus extensions or anti-tracking extensions could affect to site pages and lead to this error. In order to fix it we need to figure out what browser extension breaks the code.
Due to our logs user's browser is Mozzila Firefox. If so, the list of installed extension/addons in browser can be found in Menu => Add-ons and themes. Could please the user navigate there and send us the screenshot (it will be similar to image below)