Few minutes back i was following the MDN firefox extension tutorial on making your first firefox extension. And i did everything as it was said. But when i go to load the temporary add-on ,it throws this error as shown in the below screen-shot saying “___does not contain a valid install manifest”.
I tried to load it selecting other files in the ‘borderify’ directory but no luck…Any one please help me out here. !!!
Probably indeed an issue with your manifest. You could use something like web-ext with its linting capability or check the Browser Console for errors when loading.
thanks for responding. Actually the JSON file was not properly formatted so that was what causing the error.Its fine now . 
In my case the problem was really simple, yet not visible because of a typical setting in windows. I created the borderify.js and the manifest.json, but windows generated a borderify.js.txt and a manifest.json.txt. Renaming them solved the problem.