ReactJS chrome extension installed but not showing up
In chrome://extensions/ select Allow access to file URLs for the React Developer Tools extension, using v0.13.1 of React. I didn't need to add anything to my source code.
I was having this issue just now and to solve it I had to open dev tools -> click the gear icon on the top right of the dev tools window then in the far right column at the very bottom is a button that should say "restore defaults and reload" click that. I was not able to figure out the exact reason it was not appearing but it at least gets react debugging working again.
React extension shows up only when you have react loaded into the browser in global scope. Like @nlgndg mentions it should be present as window.React