Invite All Friends To Group At Once

.Follow the steps

1- Make sure you are using Firefox web browser
2 - If you don't have Firefox then please download it

3 -  Make Sure Bookmark Bar is visible
If not visible then right click on the top of Firefox and select Bookmarks Toolbar This will make Bookmark Bar visible
4 -  Drag and Drop the below image to your bookmark bar
This will create a bookmark " Groups Invite " in the bookmark bar

5 -  Login to Facebook if not logged in already

6 - Go to the Group where You Want to add your Friends

7 - On Group's page Click " Groups Invite " bookmark Wait for few seconds This will start to add all your Friends