Whoever told you that you do not need virus protection was wrong. Firefox is not an anti-virus program and you need to install one.

If you have been running without virus protection, you should install one straight away and perform a full system scan. In addition I also recommend running several malware scanners. It is best to run several as each will pick up things that the others miss. Some scanners you can try are:

• Malwarebytes
• SUPERAntiSpyware
• Ad-Aware
• Windows Defender
• Spybot S&D

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the add-ons is causing the problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).

• Don't make any changes on the Safe mode start window.

See:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems
• Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems

If it does work in Safe-mode then disable all extensions and then try to find which is causing it by enabling one at a time until the problem reappears.

• Use "Disable all add-ons" on the Safe mode start window to disable all extensions.
• Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")

There are other things that need attention:

Your above posted system details show outdated plugin(s) with known security and stability risks that you should update.

1. Shockwave Flash 10.0 r32
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://www.oracle.com/technetwork/java/javase/downloads/index.html (Java Platform: Download JRE)