The firewall has to update the permission for a new version of Firefox, otherwise communication would be blocked because the application has changed.

One or a few versions ago, some plumbing was added to allow Firefox to connect to videocasting devices and I think that was why Firefox wanted rules allowing it to discover those devices on your local network (or advertise to those devices perhaps). I edited those rules to block* and haven't noticed any ill effects. Later updates didn't change the rules.

If you want to block the connections, switch the rules instead of removing them:

Windows 7 Start menu > Control Panel > System and Security > Windows Firewall > (left column) Advanced Settings

In the dialog that pops up: Inbound Rules

Then double-click the Firefox rules and change to Block one by one.