I want to install java plug-in in firefox .
I read that installing java plug-in is not secure.
EDIT1 : Can anyone please tell me why java installation is not secure, and should I install it or not.
Download and install Java from java.com.
If it doesn't seem to work, check if it is installed using Java Tester. If it only doesn't work in Firefox, make sure that the Java plugin is enabled in the Add-ons Manager tab:
No nontrivial software is absolutely secure, at least when it is exposed to the Internet. Rather, software security is a relative term: Some software is more secure, other software less so.
As for java, when run as a plugin in the browser, I think it is safe to say that its security record has been rather abysmal. There have been many security holes, and though all publicly known security holes have been patched as far as I know, history does not inspire confidence.
Since you use firefox, you can improve your security somewhat by enabling
plugins.click_to_play. If you do, all plugins such as flash and java will be disabled on every web page you visit until you click on the plugin to allow it to run.
To enable this feature, type
about:config in the Firefox address bar and hit return. You may get a warning. Take it seriously! Messing around in
about:config without knowing what you're doing can really ruin your setup. Anyhow, find the option
plugins.click_to_play in the list – there is a handy search box that you can use – and double click the line to toogle the value between false and true.
See also this question, which I noticed after writing the above.