hello, both versions of the java plugin will run on all current versions of firefox: http://www.java.com/de/download/help/sysreq.xml

to keep your system save, you should update firefox and all your plugins (especially java), since old versions are vulnerable and widly get exploited on the web.

Philipp, Sorry but that does not answer my question.

I use certain websites which does not give smooth working when using latest Java 7 and firefox 23.

So i have to use Java 6 as the websites does not support Java 7 yet. So when using Java 6 with Firefox 23 the sites visited by me does not work.

So I would appreciate instead of giving me links to other pages and advise on security, if you could answer my simple question that I have asked.

then please provide more details to your question - what does "sites visited by me does not work" mean exactly (are there any error messages,...)?

Please also give links to the problem pages if they are public so that we and others may test them. You could also consider contacting the sites concerned directly yourself.

Using Java can raise security concerns,and especially so using outdated versions.

• see a couple of Mozilla blogs
  https://blog.mozilla.org/security/2013/01/11/protecting-users-against-java-vulnerability/
  https://blog.mozilla.org/decoder/2012/04/06/why-an-outdated-java-plugin-is-so-serious/
• and one of their own,noting the long list of links and security fixes.
  https://blogs.oracle.com/security/entry/july_2013_critical_patch_update

You are apparently using Firefox 15 that is not supported, not secure and putting your personal data and system at risk. Please update immediately for your own safety. Please post back if you have problems trying to do that.