There are a couple reasons it may be taking a long time to start:

• Extensions may be slowing it down. Some, including antivirus toolbars, Browser Highlighter, and Skype extension are known to cause delays. See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems.
• If you are getting delays where the status bar says "Waiting for site" or "Connecting to", make sure Firefox is fully allowed in all firewall software. See Configure firewalls so that Firefox can access the Internet

Thanks zzxc. I have no skype, no highlighter so will be looking at Norton toolbar.