You all must have heard about the Chrome browser. It's one of the most widely used Internet browser in the world. Google chrome has hundreds of Chrome Extensions, one of those extension in Invite All. Invite All lets you to Select All your Facebook Friends at once while sending them any request.
So download this Extension from here ( Download Invite All Chrome Extension ).
Then Open your chrome browser, Go to Settings, and then choose Extensions. Or you can directly open chrome://extensions/ in your browser.
Then drag and drop the Downloaded Extension file here. Chrome will automatically install it. Hurrayyy !! we are done.
Now, open your Facebook account and try sending your Friends some requests and you will find the Select All button at the bottom. Enjoy !