This indicates a problem with the file that stores preferences, for details see How to fix preferences that won't save.

You are behind on security updates of your plugins.

Your above posted system details show outdated plugin(s) with known security and stability risks.

1. Shockwave Flash 10.1 r82
2. Next Generation Java Plug-in 1.6.0_21 for Mozilla browsers

Update the Flash plugin to the latest version.

• http://www.adobe.com/software/flash/about/

Update the Java plugin to the latest version.

• http://java.sun.com/javase/downloads/index.jsp (Java Platform: Download JRE)

The second reply was a non sequitur and utterly unhelpful. Why did you bother? Some sense of superiority? Try being more HELPful, and less sanctimonious. I have EXACTLY the versions I want of each program that work best on MY computer.

Thank goodness Tony E knew the right answer and directed me to the solution. Thanks, Tony!

It is important to keep software updated to the latest versions to receive security updates.
Using old versions and Firefox 3.5.8 is also 5 versions behind on the current 3.5.13 version makes you more vulnerable than necessary to security vulnerabilities.

See:

• http://www.mozilla.org/security/known-vulnerabilities/firefox35.html
• http://www.mozilla.org/security/known-vulnerabilities/firefox36.html

Many plugins have full system access and being behind on updates of those can have more serious implications.

• http://www.adobe.com/support/security/bulletins/apsb10-22.html
• http://www.oracle.com/technetwork/java/javase/6u22releasenotes-176121.html

• https://www.mozilla.com/plugincheck/