Maybe FF upgraded so new file different.
Open the security centre and choose web and email protection. Choose firewall and Internet connections for programs and see if Firefox is shown as blocked. If so remove it or edit access.
Just add it to your firewall permissions again.
Double-click the taskbar icon to open SecurityCenter
Click Web and Email Protection
Click Program Permissions or Internet Connections for Programs (depending on your version)
It should be noted that the latest Firefox 5 disables SiteAdvisor, which is being worked on.
Thank you very very much for the explanation ... all working again.