This issue can be caused by an extension that isn't working properly.

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of your add-ons is causing your 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 and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems

Other things that need attention.
See http://www.mozilla.com/plugincheck/

Your above posted system details show outdated plugin(s) with known security and stability risks that you should update.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_18 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)

Many thanks for all your trouble and explanation I do appreciate it. but....

Im sorry I dont understand computers enough, safe start and switching themes and all that - I have no idea what that's about. There's no Mozilla safe start in my files, I tried the Flash update 3 times and my computer kept freezing up.

Im going to use Chrome as my main browser from now on and see what happens.

Much appreciate your helping though.