please tell me how to increase font size

The Firefox Page Zoom feature does a domain by domain level of saving the users preferred zoom level settings, there is no default Page Zoom level setting in Firefox.

Try the Default FullZoom Level extension:
https://addons.mozilla.org/en-US/firefox/addon/6965

Or the NoSquint extension:
https://addons.mozilla.org/en-US/firefox/addon/2592/

Other things that need attention:

Your above posted system details show outdated plugin(s) with known security and stability risks that you should update.

• Next Generation Java Plug-in 1.6.0_14 for Mozilla browsers

Update the Java plugin to the latest version.

• http://www.oracle.com/technetwork/java/javase/downloads/index.html (Java Platform: Download JRE)