Sometimes when working on your development machine and using firefox, you may get the error:


this is because firefox may block some ports by default, such as 530, 531, 540, so what would you do? remove your web application and make it on another port? well, no! you can easily unblock firefox port as follows:

Type the following in the address bar in firefox:  

about:config , you will be presented with security message telling you that changes may affect performance and security, click the button to continue.

Now right click on anywhere in the list, and choose NEW>> STRING, a window will open to enter the name for this record, type :

 now you will be presented with another window, enter the value for the port you want to unblock, such as 530. and hit OK.

 close your browser and go back to your SharePoint site and enjoy.