If you try starting in Firefox safe mode, does that work? See Diagnose Firefox issues using Troubleshoot Mode

Sorry Chris but I don't even get that far - after download latest Firefox - I cannot get the installation to work. I get dialogue box with "0% extraction" then nothing also cannot get Opera to install. The installation stalls at the same point of extracting the download. The only browser to work is IE8. I think it is more a Java problem as everything worked Ok until I took a Java upgrade.

Just to clarify, are you Terry Pegrum?

I have a mac running snow leopard -- same problem: after performing java updates for Firefox, application wouldn't open. I dumped it and am downloading a new copy... will see if that works.

Hi - yep one and the same! I have done nothing different over the last 3 days but now Firefox has decided to install and it loads just fine - I have not a clue why or what caused it as I havent downloaded a thing - but thanks for the offer of help. Regards Terry

Finally got it to work. Didn't work after first reinstall. So I trashed the preference and library files for Firefox before attempting next download/reinstall. Low and behold--it now works!

I have the same problem. I did catch IE8 blocking a file from downloading, however I do not know how to stop IE8 from doing this. It was blocked due to the mozilla website being restricted by IE8, but I can not locate where this is happening. Unfortuneately I can not get Mozilla support interested in this problem.