I had a similar problem with Kaspersky and Firefox when working on a web development project. (C # ASP is not Joomla).
I disabled the Kaspersky add-in for Firefox and disabled Web Anti-Virus in Kaspersky.
To disable web anti-virus, go to "Settings" → "Protection", and then disable "Web Anti-Virus".
I did some additional research: this can also be the result of the “Anti-Banner” function, which can also be disabled in the “Settings” → “Protection” section.
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