Make sure your Java (Not JavaScript) is up to date Verify Java and Find Out-of-Date Versions {web link}

Version 8 Update 66 Release date November 16, 2015

Use this link to check that your plugins are up-to-date. If any are listed as unknown or research, do not worry about them.

Thanks I installed a newer version but it doesn't help. I am using this site as an example:

http://www.andrewshousehotel.co.uk/

they have an old Java plugin to display some images I guess. Whole site seems out of date. In the image frame I only see "error. click for details" and then a message that an application is blocked due to my security settings. But I had this problem on a more trusted site, which uses Java to sign documents, and apparently their version was too old for my browser to accept.

I was blocked by Java security script. I've called the big guys to help you. Good luck.

Do you mean the attached message? That's not from Firefox, that's from Java itself after Firefox allows Java to run.

In this case, the lock with an exclamation point icon indicates that the site has not obtained the necessary certificate and "signed" the Java applet; this is Oracle's method of reducing the risk that rogue applets planted on hacked sites will be used to attack you. If you aren't worried about that scenario, you can make a site-specific exception.

The information link in the error dialog leads to this page: http://java.com/en/download/help/jcp_security.xml

And this page has steps for using the exception list: https://www.java.com/en/download/faq/exception_sitelist.xml

I'm assuming this Java applet isn't essential to their business, or they would have fixed this by now... I suspect it's just some kind of slide show.