That message is obviously wrong, Firefox supports Javascript. And it has nothing to do with Java in Control Panel.

Did you ask the manufacturer about this error?

One reason users might have seen that message in the past is if the site wanted to use the Flash plugin and used a script to load it. Flash is not longer supported as of a few months ago, so if the site still expects it to load, that could be one explanation.

One method to suss out an issue with settings or add-ons versus a site incompatibility is:

New Profile Test

This takes about 3 minutes, plus the time to test the problem site.

Inside Firefox, type or paste about:profiles in the address bar and press Enter/Return to load it.

Take a quick glance at the page and make a mental note of which Profile has this notation: This is the profile in use and it cannot be deleted. That is your current default profile.

Click the "Create a New Profile" button, then click Next. Assign a name like Apr2022, ignore the option to relocate the profile folder, and click the Finish button.

Firefox will switch your default profile to the new one, so click the Set as Default Profile button for your regular one to avoid an unwanted surprise at your next startup.

Scroll down to Apr2022 and click its Launch profile in new browser button.

Firefox should open a new window that looks like a brand new, uncustomized installation. (Your existing Firefox window(s) should not be affected.) Please ignore any tabs enticing you to connect to a Sync account or to activate extensions found on your system to get a clean test.

Does the problem site work any better in the new profile?

When you are done with the experiment, you can close the extra window without affecting your regular Firefox profile. (Apr2022 will remain available for future testing if needed.)

One reason users might have seen that message in the past is if the site wanted to use the Flash plugin and used a script to load it. Flash is not longer supported as of a few months ago, so if the site still expects it to load, that could be one explanation.

Flash support was removed at end of Jan 2021 as of Fx 84.0. https://support.mozilla.org/en-US/kb/end-support-adobe-flash

I have Java installed, and its Control Panel tells me that "Java in Browser is enabled", but not which one.

Why do Java, Silverlight, Adobe Acrobat and other plugins no longer work? https://support.mozilla.org/en-US/kb/npapi-plugins

The JavaScript in Firefox and the Java Plugin from Oracle are two different things. JavaScript was originally going to be called LiveScript which would have reduced the confusion with the Java Plugin. http://kb.mozillazine.org/JavaScript_is_not_Java

IE was about the only web browser that still allowed a Java Plugin to run in browser for a good while.

I need to access the SolarEdge Monitoring web site to get data from my newly installed solar PV installation.

The website at https://monitoring.solaredge.com/solaredge-web/p/login ?

The Demo-account login page with examples seems to display fine in Firefox.

jscher2000 - Support Volunteer said

One reason users might have seen that message in the past is if the site wanted to use the Flash plugin and used a script to load it. Flash is not longer supported as of a few months ago, so if the site still expects it to load, that could be one explanation.

Flash support was removed at end of Jan 2021 as of Fx 84.0. https://support.mozilla.org/en-US/kb/end-support-adobe-flash

Wow, I guess I lost a whole year!