This may be due to a problem with an add-on. Follow the procedure in the troubleshooting extensions and themes article to see if it helps.

Your above posted system details show outdated plugin(s) with known security and stability risks.

• Java Plug-in 1.6.0_01 for Netscape Navigator (DLL Helper)

Update the Java plugin to the latest version.

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

I also had this problem but managed to resolve it by disabling the antiphishing toolbar that Bitdefender had installed in Firefox.