how to know if Java is installed on my windows11

Well.. Firefox uses Javascript on websites which only gets updated when Firefox does. You can visit https://www.whatismybrowser.com/detect/is-javascript-enabled/ to see if it's enabled in Firefox. It doesn't cause a popup asking to update Java that I have ever seen.

Sounds like your system might have actual Java installed and that's what is displaying the popup. Difference: https://www.java.com/en/download/help/java_javascript.html.

I'd look in Windows' Control Panel -> Programs & Features to see if it's listed there. Might also find it in Windows' Settings -> Apps.

Hope that helps, Mark H.

The desktop Firefox web browser has not used the NPAPI Java Plugin since Firefox 52.0 Release back on March 7, 2017. https://support.mozilla.org/en-US/kb/npapi-plugins

Note the JavaScript in Firefox and the Java Plugin are two separate things. JavaScript was originally going to be called LiveScript which would have greatly reduced this confusion. https://kb.mozillazine.org/JavaScript_is_not_Java

It wouldn't hurt to do some malware scans. See the following article for tools other Firefox users have found helpful: Troubleshoot Firefox issues caused by malware.

Ooo, I that's an idea. Thank you

Thank you, PC does have Java 8- 171 So safe to update.

Thank you

Mark, thank you. this PC does have Java 6-171 (63 bit). I originally had looked under settings but missed the obvious first choice of default apps! Everyone has been so helpful.