How can it be unacceptable that software with an expired license wont work? That is to be expected surely?
Method 1: Uninstall all remnants of McAfee using the MCPR cleanup tool: http://download.mcafee.com/products/licensed/cust_support_patches/MCPR.exe
Firefox should work.
If not then uninstall Firefox and reboot, then reinstall it.
It should then seek permission via whatever firewall you are now using.
Method 2: Go to your local McAfee products page and download a trial of "VirusScan Plus" and then action the permissions in the firewall.
Then uninstall McAfee in the normal way via Control Panel
Then run the previously mentioned cleanup tool and reboot.
Note: Method 2 may entail uninstalling whatever protection software you are currently using.