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

As I help on another forum I had to delete the Firefox 4 and go back to 3.6.15 as a temporary measure since closing a tab left a ghost tab which had the possibility of being re-opened. With no indications of which were which and the live tabs having no indications as to what they were it was not possible to use as was. Try having a mix of 50 plus tabs/ghost tabs at the same time. Did as suggested after re-installing FF 4 and running in Safe mode to start with then re enabling Extensions as I went and after starting and restarting a few times everything a few times there is no problem. I have however disabled some of the extensions that are not compatible with FF 4 and these may have been the cause of some of the problems.

Thanks for your help.